Instant, exact conversion from millimeters (mm) to decimal and fractional inches ("). Engineered for machinists, 3D printing enthusiasts, woodworkers, and architects.
"Millimeters to inches" is the conversion between two units of length: the millimeter (mm), the base unit of the metric decimal system, and the inch (in), part of the imperial system. One millimeter equals exactly 0.0393701 inches, or stated directly, one inch is exactly 25.4 mm. This equivalence is essential in engineering, architecture, woodworking, and digital manufacturing.
MM to inch equivalencies show the direct relationship between metric and imperial systems for dimensional measurements across workshops, design, and manufacturing.
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One millimeter (mm) equals 0.001 m, while one inch (in / ") corresponds to 25.4 mm (2.54 cm). Measuring instruments such as calipers, tape measures, and micrometers combine both scales to guarantee exact tolerances in workshop and production.
Converting millimeters to inches takes 3 simple steps: identify the measurement, apply the exact formula, and express the final result.
Take the millimeter measurement from your caliper, technical blueprint, or workshop rule.
Apply the international exact conversion factor established by the SI standard.
Express the value in decimal inches or round to the nearest imperial workshop fraction.
The official SI formula is exact: Inches = mm ÷ 25.4. The resulting decimal easily converts into standard workshop fractions (1/2", 1/4", 1/8", 1/16", 1/32", 1/64") for carpentry, turning, and CNC machining.
Lookup standard metric dimensions with corresponding decimal and fractional inch equivalents.
| Millimeters (mm) | Inches (Decimal) | Inches (Fraction) |
|---|---|---|
| 1 mm | 0.0394" | ≈ 3/64" |
| 2 mm | 0.0787" | ≈ 5/64" |
| 3 mm | 0.1181" | ≈ 1/8" |
| 4 mm | 0.1575" | ≈ 5/32" |
| 5 mm | 0.1969" | ≈ 13/64" |
| 6 mm | 0.2362" | ≈ 15/64" |
| 6.35 mm | 0.2500" | = 1/4" |
| 8 mm | 0.3150" | ≈ 5/16" |
| 9.525 mm | 0.3750" | = 3/8" |
| 10 mm | 0.3937" | ≈ 25/64" |
| 12 mm | 0.4724" | ≈ 15/32" |
| 12.7 mm | 0.5000" | = 1/2" |
| 15 mm | 0.5906" | ≈ 19/32" |
| 16 mm | 0.6299" | ≈ 5/8" |
| 19.05 mm | 0.7500" | = 3/4" |
| 20 mm | 0.7874" | ≈ 25/32" |
| 22 mm | 0.8661" | ≈ 7/8" |
| 25 mm | 0.9843" | ≈ 63/64" |
| 25.4 mm | 1.0000" | = 1" |
| 30 mm | 1.1811" | ≈ 1 3/16" |
| 35 mm | 1.3780" | ≈ 1 3/8" |
| 38.1 mm | 1.5000" | = 1 1/2" |
| 40 mm | 1.5748" | ≈ 1 37/64" |
| 45 mm | 1.7717" | ≈ 1 25/32" |
| 50 mm | 1.9685" | ≈ 1 31/32" |
| 50.8 mm | 2.0000" | = 2" |
| 60 mm | 2.3622" | ≈ 2 23/64" |
| 70 mm | 2.7559" | ≈ 2 3/4" |
| 75 mm | 2.9528" | ≈ 2 61/64" |
| 76.2 mm | 3.0000" | = 3" |
| 80 mm | 3.1496" | ≈ 3 5/32" |
| 90 mm | 3.5433" | ≈ 3 35/64" |
| 100 mm | 3.9370" | ≈ 3 15/16" |
| 150 mm | 5.9055" | ≈ 5 29/32" |
| 200 mm | 7.8740" | ≈ 7 7/8" |
| 254 mm | 10.0000" | = 10" |
| 304.8 mm | 12.0000" | = 12" |
| 500 mm | 19.6850" | ≈ 19 11/16" |
| 1000 mm | 39.3701" | ≈ 39 3/8" |
Industries working across millimeters and inches rely on exact length conversions for engineering, manufacturing, and assembly.
Cutting, drilling, and assembly combining metric lumber dimensions with imperial drill bits and saw blades.
High-frequency measurements searched by machinists, engineers, and fabricators.
Precision tools for wrenches, sockets, drill bits, screws, pipes, pressure, and more. Each calculator includes reference tables, formulas, and industry examples.
Everything you need to know about millimeter and inch conversions, fractions, and manufacturing standards.
One millimeter equals exactly 0.03937 inches (1 ÷ 25.4), which corresponds approximately to 1/25 of an inch in fractional imperial notation.
The exact factor is 25.4 (Inches = mm ÷ 25.4). It is an exact, unrounded constant defined by the 1959 international agreement and endorsed by NIST.
Apply the same formula by dividing by 25.4. For example: 0.5 mm ÷ 25.4 = 0.0197" and 12.7 mm ÷ 25.4 = 0.5" (exactly 1/2").
25 mm equals 0.9843 inches (≈ 63/64"). Although in everyday measurements it is approximated to 1", the 0.4 mm difference is critical in manufacturing and calibration.
100 mm equals 3.9370 inches (≈ 3 15/16"), as well as 10 cm or 0.1 m. It is a standard dimension in screen sizes, lumber, and mechanical components.
Because dividing by 25.4 produces direct decimal values (0.3937"). Engineering prefers decimals for precision, while woodworking and plumbing use fractions (1/8", 1/4", 1/2").
Yes, using the exact same formula (mm ÷ 25.4). For example: 0.05 mm = 0.00197", 0.1 mm = 0.00394", and 0.2 mm = 0.00787", typical in microelectronics and micrometers.
Both represent the exact same length: decimal format uses point notation (0.5") for CAD and technical drawings, while fractional notation uses fractions (1/2") for hand tools and tape measures.
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