mm to inches calculator
Convert millimeters to inches and centimeters instantly. Enter a metric measurement and get the inch figure for US tape measures and specs.
Millimeters show up constantly on imported hardware, fastener packaging, and metric spec sheets, but US measuring tapes and lumber sizes run in inches. This calculator converts a millimeter measurement into inches and centimeters so you can match parts, order the right size, or read a metric drawing without a mental math detour.
How this calculator works
Multiply the millimeter value by the conversion factor to get inches, and divide by 10 to get centimeters.
Formula: Inches = millimeters × 0.0393701. Centimeters = millimeters ÷ 10.
Worked example
100 millimeters:
- Inches: 100 × 0.0393701 ≈ 3.937 in
- Centimeters: 100 ÷ 10 = 10.00 cm
Reference
| Millimeters | Inches | Centimeters |
|---|---|---|
| 10 mm | 0.394 in | 1.00 cm |
| 25 mm | 0.984 in | 2.50 cm |
| 50 mm | 1.969 in | 5.00 cm |
| 100 mm | 3.937 in | 10.00 cm |
Where this conversion is used
Metric bolt diameters, pipe wall thicknesses, and tile gap specs are almost always in millimeters, so this conversion gets used every time a metric part needs to fit a US-measured opening or tool. For the reverse direction on a larger scale, or when you’re working in whole inches to feet, see the CM to Inches Calculator.
Frequently asked questions
How many inches is 1 mm?
1 millimeter equals 0.0393701 inches — roughly 1/25 of an inch. It takes about 25.4 mm to make one inch.
Why convert millimeters to inches for construction?
Imported fasteners, plumbing fittings, and hardware are often spec'd in millimeters, but US tape measures, framing squares, and lumber sizes are in inches. Converting lets you check fit before you buy or cut.
Is 1 inch exactly 25.4 mm?
Yes. Since 1959 the inch has been defined as exactly 25.4 millimeters internationally, so this conversion is exact, not approximate — the only rounding happens in the displayed decimal places.
What's the centimeter figure for?
Centimeters are shown alongside inches because many metric drawings and product specs list dimensions in cm rather than mm. Dividing your mm figure by 10 gives centimeters directly.
How do I go from inches back to millimeters?
Multiply inches by 25.4. A 4-inch pipe fitting is 101.6 mm.
Estimates only. Verify quantities with your supplier before purchasing.