Paint Calculator

The paint calculator is the most essential tool for any homeowner, contractor, or DIY enthusiast planning a painting project. It removes all guesswork by computing exact paint quantities based on your room dimensions, wall height, number of coats, and surface type. Buying too little forces mid-project trips to the store; buying too much wastes money and creates hazardous leftover material that requires proper disposal.

A standard gallon of interior paint covers approximately 350 to 400 square feet of smooth wall surface in one coat. A bedroom measuring 12 × 14 feet with 9-foot ceilings requires roughly 2 gallons for two coats on walls alone. Without calculating paint needed, most homeowners either overbuy by 30% or run critically short at the worst possible moment.

Use this free Paint Calculator Suite — a 10-card interactive tool — to instantly compute gallons needed, estimate total project cost, plan drying time between coats, compare paint coverage across surface types, analyze brand durability value, calculate specialty surfaces, and even model the return on investment painting delivers to your home’s equity. No sign-up required.

The Science and Math of Paint Estimation

Accurate paint estimation is not simply a matter of measuring walls. It sits at the intersection of applied chemistry, substrate physics, and project economics. Underestimating your paint quantity causes delays — most projects require 48 to 72 hours between store visits and application, which disrupts wet-edge timing and risks visible lap marks in the finished surface. Overestimating, by contrast, generates leftover paint classified as hazardous household waste in most jurisdictions, carrying disposal costs and environmental liability.

The 10-card interactive paint suite below handles this complexity. Card 1 covers basic room coverage. Cards 2 and 3 handle multi-room project planning and cost estimation. Card 4 dives into coverage efficiency and the physics of film formation. Card 5 calculates exterior siding and trim. Card 6 models drying and recoat schedules adjusted for real-time humidity and temperature. Card 7 performs side-by-side brand durability analysis and annualized cost comparisons. Card 8 estimates leftover paint storage. Card 9 covers specialty surfaces — cabinets, decks, fences, and garage floors. Card 10 calculates the return on investment painting delivers to your home’s appraised value.

Together, this suite represents a level of calculation depth unavailable from any major retail paint brand’s online tool.

Step-by-Step Guide: How to Calculate Your Paint Needs

Step 1 — Measuring Room Perimeter and Wall Height

Measure your room length and room width in feet using a tape measure along the baseboard at floor level. Calculate gross wall area using the standard perimeter formula:

Gross Wall Area = 2 × Wall Height × (Room Length + Room Width)

For a 12 × 14 room with 9-foot ceilings: 2 × 9 × (12 + 14) = 468 square feet of gross wall area.

For irregular room shapes — L-shaped rooms, rooms with bay windows, or rooms with angled alcoves — divide the floor plan into rectangular sections, calculate each section’s wall area independently, and add the totals together before entering a combined value. For vaulted or cathedral ceilings, measure the average wall height (floor to midpoint of the slope) rather than the peak height, as the triangular upper sections above the average contribute less painted surface than a calculation to full peak height would suggest.

To calculate the total square footage of your walls accurately across complex floor plans, use our dedicated square footage calculator before entering values here.

Step 2 — Deducting Doors, Windows, and Fixed Fixtures

Enter the number of standard doors and windows in the room. The calculator automatically applies the following standard deductions used by professional estimators aligned with PCA (Painting Contractors Association) methodology:

• Standard interior door: 21 square feet deducted
• Standard window: 15 square feet deducted

Subtract additional non-painted fixed features — built-in bookshelves, fireplace surrounds, tile wainscoting, and large fixed windows — from your gross wall area to arrive at net paintable area. This is the only figure that should be divided by your coverage rate to determine gallons needed.

Net Paintable Area = Gross Wall Area − (Doors × 21 sq ft) − (Windows × 15 sq ft) − Fixed Features

Step 3 — Adjusting for the Number of Coats

Two coats is the professional industry standard for interior painting. A single coat leaves the substrate partially visible in raking light, produces uneven color saturation, and reduces the expected film durability. Three coats are required when painting bare, unprimed drywall; covering very dark existing colors with light replacements; or applying paint over stained, tannin-rich wood substrates.

Total Gallons = (Net Paintable Area ÷ Coverage Rate per Gallon) × Number of Coats

Always round up to the nearest whole can size. A 3.3-gallon calculated result becomes a 4-gallon purchase.

Understanding Paint Coverage Rates and Substrate Absorption

The Impact of Surface Porosity on Paint Spreading Rates

The coverage rate printed on a paint label — typically 350 to 400 square feet per gallon — applies only to smooth, previously painted, non-porous surfaces. The moment you apply that paint to a porous substrate, the coverage rate drops dramatically because the substrate physically absorbs the liquid carrier before the surface film can form.

Bare drywall paper absorbs paint through capillary action into the gypsum matrix below. Brick and masonry contain thousands of microscopic pores that trap paint before the binder can bridge them. Raw wood grain channels absorb paint along the growth rings before cross-grain coverage is achieved.

The practical solution in all porous cases is a bonding primer applied first. Primer seals the substrate’s pores, dramatically reducing the amount of expensive topcoat paint consumed on first contact. According to PCA Standard P1 guidelines for surface preparation, priming bare drywall before topcoat application is classified as a mandatory — not optional — preparation step for achieving warranted adhesion and coverage performance.

Coverage Rate Reference Table:

Surface Type	Coverage Rate (sq ft/gal)	Why Lower or Higher	Coats Recommended
Smooth Painted Wall	350–400	Non-porous, previously sealed	2 coats
New Drywall (Primed)	300–350	Slightly more absorbent than sealed	2 coats
Bare Drywall (Unprimed)	200–250	Very high absorption — primer required	2–3 coats
Textured Wall	250–300	Surface irregularities increase contact area	2–3 coats
Brick or Masonry	150–200	Highly porous, deep mechanical absorption	2–3 coats
Stucco	100–150	Rough texture with maximum absorption	3 coats
Wood (Sanded)	300–350	Grain absorption moderate	2 coats

Textured Substrates: Calculating Paint Volume for High-Porosity Surfaces

Rough plaster, stucco, and textured brick present a compound challenge: their pores absorb paint, AND their physical surface geometry increases the actual painted surface area beyond what simple length × height measurements capture. A deeply textured stucco wall has 20 to 40% more physical surface area than a smooth wall of identical dimensions.

For textured surfaces, apply a texture multiplier to your net square footage before dividing by coverage rate. The calculator’s Card 4 handles this automatically, but for manual estimates use these multipliers: smooth = 1.0×, light texture = 1.1×, medium orange peel = 1.15×, heavy knockdown = 1.2×, stucco = 1.25–1.3×.

Paint Sheen and Volume Solids Percentage

Paint sheen level affects not only visual appearance but coverage efficiency. Gloss and semi-gloss paints typically contain higher volume solids percentages — meaning more active pigment and binder per gallon relative to the water or solvent carrier. This higher solids content allows semi-gloss and gloss formulations to achieve coverage rates comparable to flat paints while leaving a thicker, more durable dry film behind.

The Mathematics of Paint: Volume Solids, WFT, and DFT

This section covers the professional-grade physics that governs why one gallon of paint covers 350 square feet and another covers 200 — and how to calculate it precisely using the same methods employed by commercial coating estimators.

Volume Solids Percentage

Every gallon of paint is a mixture of two components: solids (pigments and binders that remain on the wall) and carriers (water in latex paints, solvent in oil-based paints) that evaporate during drying. The Volume Solids % is the ratio of active solid material to total wet paint volume.

A paint with 40% volume solids means that when one gallon is applied and the carrier fully evaporates, only 0.4 gallons’ worth of actual film material remains on the wall. A premium paint at 55% volume solids leaves 37.5% more film per gallon — producing a thicker, more durable, better-covering coat.

Theoretical Coverage Formula (per SSPC and ASTM coating standards):

Theoretical Coverage (sq ft/gal) = (1604 × Volume Solids %) ÷ Desired Dry Film Thickness (mils)

Example: A paint with 45% volume solids applied at a 1.5-mil target dry film thickness yields: (1604 × 45) ÷ 1.5 = 48,120 ÷ 1.5 = 320.8 sq ft per gallon theoretical coverage.

Wet Film Thickness (WFT) vs. Dry Film Thickness (DFT)

Wet Film Thickness (WFT) is the physical depth of the wet paint layer immediately after application, measured in mils (thousandths of an inch) using a wet film gauge notched comb. Dry Film Thickness (DFT) is the final cured film depth after all carrier has evaporated, also measured in mils.

The relationship between them is governed by the volume solids percentage:

DFT = (WFT × Volume Solids %) ÷ 100

Example: Applying paint at 4 mils WFT with 40% volume solids yields: (4 × 40) ÷ 100 = 1.6 mils DFT.

Professional painters use a wet film gauge comb during application to verify they are hitting the target WFT specified by the manufacturer. This practice is particularly important on commercial projects where the paint manufacturer’s warranty is contingent on meeting specified dry film thickness — typically 1.2 to 2.0 mils DFT for interior latex coatings.

The Chemistry of Coalescence: Why Paint “Dries”

Latex paint does not simply “dry” — it undergoes a two-stage chemical process called coalescence. In Stage 1, the water carrier evaporates from the wet film, concentrating the suspended acrylic binder particles. In Stage 2, the concentrated binder particles fuse together under the pressure of surface tension into a continuous, flexible, durable polymer film. This fusion is coalescence.

This chemistry explains precisely why high humidity is so damaging to paint jobs: when relative humidity above 70% slows the evaporation rate of water from the film, Stage 1 drags on, delaying Stage 2. The binder particles remain isolated longer, producing a weaker, more porous, less adhesive film with visible sheen inconsistencies. It also explains why Volatile Organic Compounds (VOCs) — the solvents in oil-based and some hybrid paints — must evaporate before the resin can cure, making ventilation critical for both finish quality and occupant safety.

The Psychrometrics of Paint Curing: Humidity, Temperature, and Dew Point

Paint curing is a microclimatic event. The temperature, relative humidity, and dew point of the air surrounding a freshly applied film control whether that film cures into a hard, durable surface or a soft, tacky, adhesion-prone failure.

How Humidity and Temperature Alter Recoat Windows

The recoat time printed on a paint label assumes application conditions of 77°F and 50% relative humidity. Real conditions are rarely ideal. The following relationships apply to all latex (water-based) paints:

Temperature effects:

• Below 50°F: Latex binders lose their ability to coalesce. The polymer chains cannot fuse correctly, leaving a brittle, chalky, structurally weak film that will peel within months. Never apply latex paint to exterior surfaces when temperature is forecast to drop below 50°F within 24 hours.
• Above 85°F: Rapid evaporation causes the surface skin to form before the wet paint beneath has released its water, trapping moisture and producing bubbling, wrinkling, or blistering.

Relative humidity effects:

• Below 30% RH: Very rapid drying causes brush drag, poor flow-and-leveling, and visible lap marks as previously applied sections skin over before the next brush pass reaches them.
• Above 70% RH: Extended open time sounds helpful but actually disrupts coalescence by preventing proper water evaporation. Recoat windows extend by 30 to 90 minutes per 10% RH above 70%.
• Above 85% RH: Do not paint. Condensation risk on surfaces makes adhesion failure likely.

Dew Point Rule: Never paint any surface — interior or exterior — when the surface temperature is within 5°F of the dew point temperature. Dew point condensation on the substrate creates an invisible moisture layer between the paint and the wall, guaranteeing adhesion failure.

Revised Recoat Wait Times Under Actual Conditions:

Paint Type	77°F / 50% RH	65°F / 65% RH	55°F / 75% RH
Latex / Water-Based	4 hours	5–6 hours	8–10 hours
Oil-Based	24 hours	28–32 hours	36–48 hours
Chalk Paint	1–2 hours	2–3 hours	4–5 hours
Water-Based Primer	1–3 hours	2–4 hours	4–6 hours

Card 6 of this calculator accepts your current temperature, relative humidity, and surface temperature inputs to compute a real-time adjusted recoat schedule for your specific conditions.

Estimating Siding and Trim Paint

Exterior painting projects require two separate calculations: siding (large flat surfaces) and trim (linear running elements including fascia, soffit, window casings, and door casings).

The 1,000 Square Foot Benchmark

A useful professional benchmark: a 1,000-square-foot exterior wall area requires approximately 3.3 gallons of exterior paint per coat on smooth vinyl siding at 300 sq ft per gallon. On rough cedar clapboard or stucco, the same area requires 5 to 6.7 gallons per coat due to texture absorption. Two full coats on 1,000 sq ft of rough siding can consume 10 to 13 gallons — a significant underestimate risk for homeowners using smooth-surface coverage rates.

Siding Calculations Based on Material Texture

Siding Type	Coverage Rate	Notes
Smooth Vinyl Siding	300–350 sq ft/gal	Lowest absorption
Smooth Hardboard	280–320 sq ft/gal	Slightly more porous
Rough-Sawn Cedar	200–250 sq ft/gal	High grain absorption
T1-11 Plywood	200–250 sq ft/gal	Groove channels add area
Stucco	100–150 sq ft/gal	Maximum texture absorption
Brick (painted)	150–200 sq ft/gal	Mortar joints absorb heavily

Before any exterior paint project, surface preparation including power washing is essential for adhesion. Use our pressure washing estimate and preparation costs calculator to plan surface prep costs before calculating paint quantities.

Trim, Fascia, and Soffit Calculations

Trim paint is calculated by linear footage, not square footage. Measure the total running feet of all fascia boards, soffit panels, window casings, door casings, corner boards, and frieze boards. Apply the width in inches of each element to convert linear footage to square footage, then divide by the trim paint coverage rate.

One quart of trim paint covers approximately 100 linear feet of standard 3.5-inch baseboard with two coats. For exterior fascia at 6 inches wide, one gallon covers approximately 160 linear feet per coat.

Specialty Projects: Cabinets, Decks, Fences, and Garage Floors

Kitchen Cabinets: Linear Runs and Surface Multipliers

Cabinet painting cannot be estimated using room perimeter formulas. Cabinets have multiple painted surfaces per linear foot of run: the door face, the door back (if painted), the face frame, drawer fronts, end panels, and interior box surfaces. Professional cabinet estimators use a linear-foot surface multiplier of 8 to 12 sq ft of actual painted surface per linear foot of cabinet run.

A kitchen with 20 linear feet of upper and lower cabinets combined has approximately 160 to 240 square feet of total painted cabinet surface. At 300 sq ft per gallon for cabinet-specific enamel paint, two coats requires 1.1 to 1.6 gallons of topcoat — plus separate quarts of deglosser and high-adhesion primer applied first.

Cabinet painting requires: (1) degloss solvent wipe-down, (2) scuff sanding to 180-grit, (3) shellac-based or bonding primer coat, (4) two topcoats of cabinet-specific alkyd enamel or waterborne acrylic enamel. Each layer is calculated separately.

Decks and Fences: Penetrating Stains vs. Film-Forming Paints

Raw wood decks and fences present a choice between two fundamentally different product types with very different coverage rates:

Penetrating semi-transparent stains absorb into the wood grain rather than forming a surface film. Coverage: 150–200 sq ft per gallon on rough-sawn wood. They require reapplication every 2–3 years but never peel because there is no film to fail.

Solid-color deck paints and opaque stains form a surface film like standard paint. Coverage: 200–300 sq ft per gallon. They provide richer color but peel and require stripping when they fail — typically every 3–5 years on horizontal deck surfaces exposed to foot traffic, UV, and moisture cycling.

For baluster-heavy deck railings, calculate each baluster’s four faces individually (typically 2 × 3.5 inches × 36 inches each) and add to the total rail and post surface area.

Garage Floors: Preparing Concrete for Epoxy Coatings

Garage floor epoxy coatings are thick, high-solids products (often 50 to 75% volume solids) applied at higher wet film thicknesses than wall paint. Standard two-part epoxy floor coatings cover 200 to 300 square feet per gallon when applied at the recommended 8 to 10 mil WFT, yielding a 4 to 7.5 mil DFT.

Critical preparation: concrete must be acid-etched (muriatic acid diluted 1:10 in water) or mechanically ground to achieve a CSP (Concrete Surface Profile) of 2 to 3, which provides the mechanical anchor profile for epoxy adhesion. Smooth, untreated concrete causes epoxy delamination within 6 to 18 months regardless of product quality.

Bulk vs. Retail: The Mathematics of 5-Gallon Buckets vs. Single Gallon Cans

For projects requiring 4 or more gallons of the same color, a 5-gallon bucket is almost always the economical choice. The typical price differential:

• 5 single gallons of mid-range interior paint: approximately $250–$350
• One 5-gallon bucket of the same paint: approximately $175–$250
• Savings per project: $75 to $100, or 25 to 30%

Beyond cost, a 5-gallon bucket offers an important consistency advantage: all paint comes from a single production batch, eliminating the subtle color variations that can occur between separately manufactured gallons even of the same tint formula. Professional painters always “box” paint — pouring multiple cans together into a single large bucket and stirring — before beginning a project for this reason.

For projects under 3 gallons, single cans are appropriate. For projects exceeding 4 gallons of a single color, always purchase a 5-gallon bucket.

Estimating Material and Labor Costs

Paint Cost Estimation Formula

Total Material Cost = Gallons Needed × Price Per Gallon

Paint pricing tiers by quality level:

• Budget/contractor grade: $25–$45 per gallon (low volume solids, typically 35–40%)
• Mid-range consumer grade: $50–$70 per gallon (moderate volume solids, 40–48%)
• Premium grade: $70–$90 per gallon (high volume solids, 50–60%)

The Annualized Cost of Durability: Why Premium Paint Is Cheaper

This is the most financially important calculation most homeowners never perform. The comparison between budget and premium paint must account for lifespan, not just upfront price.

Annualized Cost Formula:

Annual Cost = (Gallons × Price Per Gallon + Labor Cost) ÷ Expected Lifespan in Years

Practical Example — 400 sq ft bedroom, two coats:

	Budget Paint ($35/gal, 5-yr life)	Premium Paint ($75/gal, 15-yr life)
Gallons needed	2.3 gallons	2.0 gallons (better coverage)
Material cost	$80.50	$150.00
DIY labor (4 hrs × $25/hr)	$100	$100
Total project cost	$180.50	$250.00
Annualized cost	$36.10/year	$16.67/year

The premium paint costs 54% less per year despite a higher upfront price. This calculation — built into Card 7 of the suite — explains why professional painters and property managers consistently specify premium paint for high-traffic surfaces.

Labor Cost Estimation

Professional painters charge $2 to $6 per square foot for interior painting, including labor and materials. A 400 sq ft room costs approximately $800 to $2,400 professionally painted. DIY painting costs only materials — typically $80 to $180 in paint for the same room — but requires 4 to 8 hours of personal time plus preparation and cleanup.

Curb Appeal Economics: Calculating Paint Return on Investment (ROI)

Painting delivers one of the highest returns on investment of any home improvement project because it transforms buyer and appraiser perception at a relatively low material cost.

Interior Painting ROI: According to real estate data consistently cited by appraisers, fresh neutral interior paint increases perceived home value by $1,500 to $3,000 for a typical 3-bedroom home at a material-only cost of $400 to $800 — representing a 200 to 400% return on material investment.

Exterior Painting ROI: Exterior painting has been cited in Remodeling Magazine’s Cost vs. Value reports as returning 50 to 150% of project cost in appraised value increase, depending on regional market conditions and paint quality level. More importantly, homes with freshly painted exteriors spend significantly fewer days on market — typically 10 to 20 fewer days — which has compounding financial value in terms of carrying cost savings (mortgage payments, insurance, taxes) during the listing period.

ROI Calculation Formula (Card 10):

Net ROI = (Estimated Value Increase − Total Project Cost) ÷ Total Project Cost × 100

Example: $600 exterior paint project on a home where fresh paint adds $2,000 in appraisal value: ($2,000 − $600) ÷ $600 × 100 = 233% ROI.

For a whole-room renovation, pair this paint ROI analysis with flooring coverage requirements and carpet installation estimation to model comprehensive room renovation returns.

Room-by-Room Paint Quantity Guide

How Much Paint Does a Bedroom Need?

A standard 12 × 12 bedroom with 8-foot ceilings has approximately 384 gross square feet of wall area. After subtracting one door (21 sq ft) and two windows (30 sq ft), net wall area is roughly 333 square feet. Two coats of standard interior paint require approximately 2 gallons for walls plus 1 quart for the ceiling (144 sq ft ÷ 400 sq ft/gal).

How Much Paint Does a Living Room Need?

A living room measuring 16 × 20 feet with 9-foot ceilings has approximately 648 square feet of gross wall area. Subtracting two doors (42 sq ft) and three windows (45 sq ft) yields approximately 561 net square feet. Two coats require approximately 3.5 gallons for walls and 1 gallon for the ceiling (320 sq ft ÷ 400 sq ft/gal).

How Much Paint Does a Bathroom Need?

Small bathrooms measuring 5 × 8 feet with 8-foot ceilings have approximately 208 gross square feet of wall area. After deducting the door and window, net area is approximately 173 sq ft. One gallon of semi-gloss or satin finish covers a full bathroom with two coats. Semi-gloss is the professional standard for bathrooms — its high sheen resists moisture, allows cleaning of soap residue and mildew, and holds up to high-humidity environments. Flat paint should never be used in bathrooms because it absorbs moisture and mildew.

Exterior House Paint Quantity

A 1,500 sq ft single-story home has approximately 1,200 square feet of exterior wall area after deducting windows and doors. At 300 sq ft per gallon for exterior paint on smooth siding, two full coats require approximately 8 gallons for walls plus 2 gallons for trim. Add a 10% waste buffer for roller splatter, brush losses, and touch-ups: 11 gallons total purchase.

Paint Finishes and Their Best Uses

Finish Type	Sheen Level	Best Room	Durability
Flat / Matte	None	Ceilings, low-traffic areas	Low
Eggshell	Very Low	Living rooms, bedrooms	Medium
Satin	Low-Medium	Kitchens, family rooms	Medium-High
Semi-Gloss	Medium-High	Bathrooms, trim, cabinets	High
Gloss	High	Doors, furniture, accents	Very High

Interior vs. Exterior Paint Coverage: Exterior paint is formulated for UV resistance and weather durability, typically covering 250–350 sq ft per gallon due to a thicker pigment load and higher binder content. Never use interior paint outdoors — it lacks the polymer flexibility to expand and contract with daily and seasonal temperature changes, causing cracking and peeling within the first year.

Common Paint Calculator Mistakes to Avoid

Mistake 1 — Using Gross Area Instead of Net Paintable Area. Always subtract doors, windows, and fixed non-painted features. Gross area inflates your estimate by 10 to 20% in a typical room.

Mistake 2 — Ignoring Surface Porosity. Applying a coverage rate of 400 sq ft per gallon to bare drywall or unprimed wood will leave you severely short. Identify your surface condition first.

Mistake 3 — Skipping Primer on Bare Substrates. Per PCA Standard P1, primer on bare drywall, wood, and masonry is a required preparation step — not optional. Skipping primer on bare surfaces results in uneven sheen, poor adhesion, and inadequate coverage from topcoats.

Mistake 4 — Not Adding a Waste Buffer. Add 10% to all paint estimates. Waste sources include roller nap absorption (a 3/8-inch nap roller holds approximately 6 oz of paint), brush drips, tray losses, container cling (approximately 2–3 oz per gallon can), overspray atomization (if spraying), and touch-up needs after furniture is returned to the room.

Mistake 5 — Painting in Wrong Conditions. Check temperature, relative humidity, and dew point before starting. Card 6 performs this analysis automatically for your conditions.

Mistake 6 — Ignoring Coat Drying Times. Recoating over insufficiently dried paint causes lifting, wrinkling, and sheen disruption. Refer to Card 6’s psychrometric drying schedule for real-time adjusted recoat windows.

Benefits of Using This Paint Calculator Suite

• 10-card modular design — covers every project type from a single room to a whole-house exterior
• Exact room coverage calculation — walls, ceiling, and trim computed separately for precision
• Surface type adjustment — coverage rate automatically corrects for porosity and texture using multipliers
• Multi-coat support — single, double, or triple coat quantities calculated instantly
• Door and window deduction — net paintable area computed after automatic surface subtractions
• Psychrometric drying planner — real-time adjusted recoat windows based on your actual temperature and humidity
• Brand durability analysis — annualized cost comparison across paint quality tiers (Card 7)
• Specialty surface calculator — cabinets, decks, fences, and garage floors (Card 9)
• Real estate ROI estimator — models home equity value increase from interior and exterior paint investment (Card 10)
• Project cost estimation — total material and labor cost displayed at your selected price per gallon
• Waste buffer option — 10% overage added automatically for professional-grade accuracy
• No registration required — completely free to use with immediate results

Frequently Asked Questions

How much paint do I need for a 12×12 room?

A 12×12 room with 8-foot ceilings requires approximately 2 gallons of interior paint for two coats on walls, plus one quart for the ceiling. Deducting one door and two windows from the gross 384 sq ft wall area leaves approximately 333 net paintable square feet — covered by two gallons at standard coverage rates.

How many square feet does a gallon of paint cover?

A gallon of interior paint covers 350 to 400 square feet per coat on smooth, previously painted surfaces. Rough, textured, or porous surfaces reduce coverage to 100 to 300 square feet per gallon depending on porosity. Always use the coverage rate and volume solids percentage on your specific paint can for the most accurate calculation.

Do I need primer before painting?

Primer is required when painting bare drywall, bare wood, after repairing holes or patches, switching from dark to very light colors, or painting over stains. Per PCA Standard P1, primer seals porous surfaces and dramatically improves paint coverage efficiency, often reducing the number of topcoats needed from three to two.

How do I calculate paint for ceilings separately?

Ceiling area equals room length multiplied by room width. A 12×14 room has a 168 sq ft ceiling. At 400 sq ft per gallon for flat ceiling paint, one gallon covers two full coats. Purchase a separate flat white ceiling paint rather than using wall paint — ceiling formulations have higher viscosity to reduce drip and spatter.

What is the best paint finish for a bathroom?

Semi-gloss is the professional standard for bathrooms. Its high sheen resists moisture, allows easy cleaning of soap and mildew, and holds up to high-humidity environments. Satin is acceptable for low-humidity powder rooms. Flat paint must never be used in bathrooms.

How much does it cost to paint a room yourself?

DIY interior painting costs $80 to $180 in paint materials for a standard bedroom. Adding painter’s tape, roller covers, brushes, and drop cloths brings total supply costs to $120 to $250 per room — compared to $800 to $2,400 for professional painting.

How do I calculate paint for an exterior house?

Measure each exterior wall width and multiply by wall height. Add all four wall totals and subtract all window and door openings. Divide by your exterior paint coverage rate (typically 250–350 sq ft per gallon based on siding texture) and multiply by the number of coats. Add 10% waste buffer. Before painting, calculate your pressure washing estimate and preparation costs for a complete project budget.

How does humidity affect paint drying time?

Relative humidity above 70% significantly extends recoat windows by slowing coalescence of the latex binder. At 75% RH and 65°F, a latex paint with a standard 4-hour recoat time printed on the label may require 7 to 9 hours between coats. Card 6 of this suite calculates your adjusted recoat window automatically based on real-time conditions.