Calcometry
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Mm to Inches Converter
Convert millimeters to inches (and back) instantly. Useful for 3D printing, bolts, and precision measurements.
Millimeters
mm
Inches
in
1 mm = 0.03937 in
Convert Millimeters
Quick presets
Inches
1 in
25.4 mm = 1 in
- 1 mm
- 0.03937 in
- 3 mm
- 0.11811 in
- 6 mm
- 0.23622 in
- 10 mm
- 0.393701 in
- 25.4 mm
- 1 in
- 50 mm
- 1.9685 in
- 100 mm
- 3.937 in
- 210 mm
- 8.2677 in
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Millimeters vs inches
Millimeters are the everyday metric unit for small lengths — hardware, manufacturing, and paper thickness. Inches are still standard for many US tools and fittings. One inch equals exactly 25.4 millimeters.
Common questions
My 3D printer slicer uses mm but the part spec is in inches — what do I do?
Convert the inch dimensions to mm before modeling or scaling. Example: 0.5 in → 12.7 mm. Slicers assume mm by default; entering inches without converting will print the wrong size.
Are M6 bolts 6 mm in diameter?
Yes — the “M6” ISO metric designation means 6 mm nominal outer thread diameter. US #6 screws are a different system; do not mix metric mm sizing with US screw gauge numbers.
How thick is 3 mm in inches?
3 mm is about 0.118 in — roughly 1/8 inch for rough work, but not exact. For gasket shims or press fits, use the precise conversion rather than fractional inch approximations.
Is A4 paper width easy to convert to inches?
A4 is 210 mm wide — exactly 8.27 in. US Letter is 8.5 in wide. The 0.23 in difference matters for printers, binders, and slide templates.