MM to Inches Converter
Convert millimetres to inches instantly. Free online mm to inch calculator with common conversion table and formula.
Formula
inches = mm ÷ 25.4
Common Conversions
How to Convert Millimetres to Inches
1 mm = 0.03937 inches. Divide millimetres by 25.4 (or multiply by 0.03937) to get inches. So 100 mm ÷ 25.4 = 3.94 in. The exact factor: 1 inch = 25.4 mm by international agreement, so the inverse is 1/25.4 = 0.039370...
Most common for engineering and DIY work where European materials use mm and American specifications use fractional inches. A 12 mm drill bit ≈ 15/32 in (0.469 vs 0.472 - very close). Construction drawings, screw sizes, and pipe diameters are the typical contexts.
Common Millimetres to Inches Conversions
| Millimetres | Inches |
|---|---|
| 1 mm | 0.04 in |
| 5 mm | 0.20 in |
| 10 mm | 0.39 in |
| 25 mm | 0.98 in |
| 50 mm | 1.97 in |
| 100 mm | 3.94 in |
| 200 mm | 7.87 in |
| 500 mm | 19.69 in |
Frequently Asked Questions
Why does engineering use mm not cm?
mm gives whole-number precision for typical part sizes (M6 bolt = 6 mm diameter). cm would mean decimal values for the same parts (0.6 cm). Whole numbers are easier to specify and avoid decimal-place errors in technical drawings.
What's a common screw size in inches?
A 3 mm screw ≈ 1/8 in, 6 mm ≈ 1/4 in, 12 mm ≈ 1/2 in. Some fasteners are sold in either standard - look for 'metric' or 'imperial' on packaging. Don't mix the two in a single project; threads don't match between systems.
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