Last updated: March 19,2026
MM to Inches Conversion
Millimeters to Inches Converter — mm to Inches Chart & Formula
The millimeters to inches converter converts any mm value to inches instantly. One millimeter equals 0.03937 inches — divide millimeters by 25.4 to convert (formula: inches = mm ÷ 25.4). For example, 10mm = 0.3937 inches and 25.4mm = exactly 1 inch. The reverse inches to mm conversion is also included below. Used worldwide in engineering, manufacturing, woodworking, and jewelry. No sign-up required — free and instant.
mm to Inches Conversion Chart — Common Values
The most common millimeter to inches conversions are listed in the table below — referenced from the International Bureau of Weights and Measures (BIPM) SI unit definition: 1 inch = 25.4 mm exactly.
| mm | Inches (decimal) | Inches (fraction) |
| 1 mm | 0.0394 in | 3/64″ |
| 2 mm | 0.0787 in | 5/64″ |
| 5 mm | 0.1969 in | 13/64″ |
| 10 mm | 0.3937 in | 25/64″ |
| 15 mm | 0.5906 in | 19/32″ |
| 20 mm | 0.7874 in | 25/32″ |
| 25 mm | 0.9843 in | 63/64″ |
| 25.4 mm | 1.0000 in | 1″ |
| 30 mm | 1.1811 in | 1 3/16″ |
| 50 mm | 1.9685 in | 1 31/32″ |
| 100 mm | 3.9370 in | 3 15/16″ |
| 150 mm | 5.9055 in | 5 29/32″ |
| 200 mm | 7.8740 in | 7 7/8″ |
| 250 mm | 9.8425 in | 9 27/32″ |
| 300 mm | 11.8110 in | 11 13/16″ |
| 500 mm | 19.6850 in | 19 11/16″ |
| 1000 mm | 39.3701 in | 39 3/8″ |
What Is Millimeters to Inches Conversion?
Definition — mm to Inches
One millimeter equals exactly 0.03937 inches — divide millimeters by 25.4 to convert to inches. Defined by the International Bureau of Weights and Measures: 1 inch = 25.4 mm exactly.
The millimeter (mm) is a unit of length in the International System of Units (SI), equal to one thousandth of a meter. The inch is an imperial and US customary unit defined since 1959 as exactly 25.4 millimeters. This exact definition makes mm to inches conversion a precise mathematical operation with no rounding ambiguity for the base conversion factor.
The mm to Inches Formula
FORMULA: inches = mm ÷ 25.4
EXAMPLE: 10 mm ÷ 25.4 = 0.3937 inches
REVERSE: mm = inches × 25.4
What Does 10mm Equal in Inches?
10 millimeters equals 0.3937 inches — calculated as 10 ÷ 25.4 = 0.393701 inches. In fractional inches, 10mm is approximately 25/64 inch. Millimeters are the standard unit across all ISO metric engineering tolerances, while inches remain standard in the US for construction and manufacturing.
mm to Inches vs Inches to mm — Key Difference
Converting mm to inches: divide by 25.4 (example: 50mm ÷ 25.4 = 1.9685 inches). Converting inches to mm: multiply by 25.4 (example: 2 inches × 25.4 = 50.8mm). Use our free inches to mm converter for the reverse calculation.
How to Use the mm to Inches Calculator (Step-by-Step)
- Step 1 — Enter your millimeter value in the input field above.
- Step 2 — The inches result appears instantly — no button needed.
- Step 3 — Read both the decimal inches value and the fractional inches equivalent.
- Step 4 — Use the mm to inches chart above to cross-reference common values.
mm to Inches — Common Applications by Industry
Millimeter to inch conversions are required across multiple industries where metric and imperial measurement systems overlap:
- Engineering & Manufacturing: ISO metric tolerances (mm) converted to ANSI inch standards for US component compatibility.
- Woodworking & Carpentry: European wood dimensions (mm) converted to inches for US lumber compatibility.
- Jewelry Making: Ring sizes, stone dimensions, and wire gauges converted between mm and inch measurements.
- Medical Devices: Catheter diameters, needle gauges, and implant dimensions converted for international standards.
- Photography & Printing: Lens diameters (mm) and print sizes converted to inch equivalents for US market specifications.
Inches to mm Conversion — Reverse Formula
The reverse of mm to inches is inches to mm. One inch equals exactly 25.4 millimeters — multiply inches by 25.4 to convert. The most common inches to mm values: 1 inch = 25.4mm | 2 inches = 50.8mm | 6 inches = 152.4mm | 12 inches = 304.8mm. Use our free inches to mm converter for quick reverse conversions.
Frequently Asked Questions — mm to Inches
How many mm in an inch?
One inch equals exactly 25.4 millimeters. To convert inches to mm, multiply by 25.4.
How to convert mm to inches?
Divide millimeters by 25.4. Formula: inches = mm ÷ 25.4. Example: 10mm ÷ 25.4 = 0.3937 inches.
What is 1mm in inches?
1 millimeter equals 0.03937 inches, or approximately 5/128 inch. This is about the thickness of a credit card.
What is 10mm in inches?
10 millimeters equals 0.3937 inches, approximately 25/64 of an inch or just under 13/32 inch.
What is 25mm in inches?
25 millimeters equals 0.9843 inches — approximately 1 inch (exact: 25.4mm = 1 inch).
What is 25.4mm in inches?
25.4 millimeters equals exactly 1 inch. This is the precise international definition: 1 inch = 25.4 mm exactly.
Is 5mm equal to 1/4 inch?
No. 5mm equals 0.1969 inches, which is approximately 13/64 inch — slightly less than 1/4 inch (which is 6.35mm).
What is mm to inches chart used for?
An mm to inches chart is used in engineering, woodworking, jewelry making, and manufacturing to quickly convert metric millimeter measurements to imperial inch values.
Final Thoughts
The mm to inches conversion is defined by a single exact factor: 1 inch = 25.4 millimeters, established by international agreement in 1959. This converter applies the precise formula (inches = mm ÷ 25.4) with no approximation. For related conversions, use our free centimeters to feet converter or our meters to feet converter for larger distance conversions within the same length cluster.