Millimeters to Inches Converter
Convert between millimeters and inches with fractional inch output. Essential for woodworking, machining, engineering, and precision manufacturing where both metric and imperial measurements are used.
mm → Inches
Inches → mm
mm to Inches Conversion Table
| mm | Inches (decimal) | Inches (fraction) | mm | Inches (decimal) | Inches (fraction) |
|---|---|---|---|---|---|
| 1 | 0.0394 | ≈ 1/32" | 15 | 0.5906 | ≈ 19/32" |
| 2 | 0.0787 | ≈ 5/64" | 16 | 0.6299 | ≈ 5/8" |
| 3 | 0.1181 | ≈ 1/8" | 18 | 0.7087 | ≈ 23/32" |
| 4 | 0.1575 | ≈ 5/32" | 19 | 0.7480 | ≈ 3/4" |
| 5 | 0.1969 | ≈ 13/64" | 20 | 0.7874 | ≈ 25/32" |
| 6 | 0.2362 | ≈ 15/64" | 22 | 0.8661 | ≈ 7/8" |
| 8 | 0.3150 | ≈ 5/16" | 25.4 | 1.0000 | 1" |
| 10 | 0.3937 | ≈ 25/64" | 30 | 1.1811 | 1 3/16" |
| 12 | 0.4724 | ≈ 15/32" | 50 | 1.9685 | ≈ 2" |
| 13 | 0.5118 | ≈ 1/2" | 100 | 3.9370 | 3 15/16" |
Common Drill Bit Sizes: mm and Inches
| mm | Inches | Nearest Fractional | Common Use |
|---|---|---|---|
| 1.0 | 0.0394" | — | Electronics, jewelry |
| 2.0 | 0.0787" | 5/64" | Pilot holes, small screws |
| 3.0 | 0.1181" | 1/8" | #6 screw pilot hole |
| 4.0 | 0.1575" | 5/32" | #8 screw pilot hole |
| 5.0 | 0.1969" | 13/64" | #10 screw pilot hole |
| 6.0 | 0.2362" | 15/64" | 1/4" bolt clearance |
| 8.0 | 0.3150" | 5/16" | 5/16" bolt clearance |
| 10.0 | 0.3937" | 25/64" | 3/8" bolt clearance |
| 12.0 | 0.4724" | 15/32" | 1/2" bolt clearance |
Drill bits are sold in both metric (mm) and imperial (fractional inch) sets. When a metric drill bit isn't available, use the nearest fractional inch equivalent. For precision work, the decimal equivalent must match within ±0.002".
Understanding Millimeters and Inches
The millimeter (mm) is one-thousandth of a meter and one-tenth of a centimeter — it's the standard precision measurement unit in engineering, manufacturing, and science worldwide. The inch is defined as exactly 25.4 millimeters since the 1959 international yard and pound agreement. This means there are exactly 25.4 mm per inch — not an approximation, but an exact defined ratio.
Millimeter-to-inch conversion is critical in machining, woodworking, 3D printing, and any field where metric and imperial components must interface. Metric fasteners (M4, M6, M8 bolts) don't fit imperial holes, and vice versa — a 5mm bolt requires a 5.0mm hole, not a 13/64" hole (which is 5.16mm). Even 0.16mm of difference can cause fit problems in precision assembly.
Where mm-to-Inch Conversion Matters Most
Woodworking and construction: Lumber is sold in imperial dimensions in the US but many power tools (especially European brands like Festool, Bosch) use metric measurements. Sheet goods thickness varies: 3mm ≈ 1/8", 6mm ≈ 1/4", 12mm ≈ 1/2", 18mm ≈ 3/4".
3D printing: Most 3D printers use metric dimensions. Nozzle sizes (0.4mm standard), filament diameter (1.75mm or 2.85mm), and layer height (0.1-0.3mm) are all in millimeters. Design files from US sources may use inches.
Automotive: Japanese and European vehicles use metric fasteners exclusively. American vehicles have transitioned to mostly metric since the 1980s but retain some imperial components. Having both metric and SAE wrench sets is essential.
For larger-scale length conversions, use our cm to Inches Converter and Feet to Meters Converter. For area calculations using these measurements, see the Square Footage Calculator and Area Calculator.
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