MM to Inches Converter — Millimeters to Inches Calculator

What Is a Millimeters to Inches Converter?

The millimeter-to-inch conversion is crucial in precision fields: engineering and machining (tolerances are often specified in mm), jewelry (ring sizes, stone dimensions), firearms (caliber measurements), and electronics (PCB component spacing). Woodworkers frequently convert between metric drill bits and imperial measurements. The conversion between these small units requires precision — even a 1mm error at this scale can be significant.

The Conversion Formula

The formula to convert millimeters to inches is:

Inches = Millimeters × 0.0393701

The reverse formula is: Millimeters = Inches × 25.4

Millimeters to Inches Reference Table

Millimeters (mm)	Inches (in)
1 mm	0.039 in
2 mm	0.079 in
3 mm	0.118 in
4 mm	0.157 in
5 mm	0.197 in
6 mm	0.236 in
8 mm	0.315 in
10 mm	0.394 in
12 mm	0.472 in
15 mm	0.591 in
20 mm	0.787 in
25 mm	0.984 in
30 mm	1.181 in
40 mm	1.575 in
50 mm	1.969 in
75 mm	2.953 in
100 mm	3.937 in
150 mm	5.906 in
200 mm	7.874 in
300 mm	11.811 in

How to Use This Converter

Enter your millimeters value in the input field above.
View the result — the inches equivalent appears instantly.
For manual conversion, use the formula: Inches = Millimeters × 0.0393701.
Check the reference table above for 20 pre-calculated common values.

Conversion Tips

Divide millimeters by 25.4 for exact inches. For quick estimation: divide by 25. So 10mm is about 0.4 inches (actual: 0.394). Precision to 0.01 inches requires the exact factor.
Rainfall is reported in millimeters in most countries and inches in the US. Key benchmarks: 25mm = 1 inch (significant rain), 50mm = 2 inches (heavy rain), 100mm = 4 inches (potential flooding).
Drill bit sizes in metric (mm) vs imperial (inches) do not align neatly. A 6mm drill bit is not the same as a 1/4 inch (6.35mm). When a project requires specific hole sizes, match the measurement system to the hardware.

Related Conversions

All conversions are calculated client-side in your browser. No data is sent to any server. For the authoritative source on unit definitions, see the National Institute of Standards and Technology (NIST).

Frequently Asked Questions

How many inches are in a millimeter?

One millimeter equals approximately 0.03937 inches, or roughly 1/25 of an inch. The exact conversion is 1 inch = 25.4 mm.

What common items are measured in millimeters?

Jewelry (ring band width, gemstone dimensions), bullet calibers (9mm), film gauges (35mm), socket wrench sizes, and precision engineering components are commonly measured in millimeters.

How do I convert mm to fractional inches for woodworking?

Convert mm to decimal inches first (mm × 0.03937), then find the nearest fraction. For example, 6mm = 0.236 inches ≈ 15/64 inch. Many woodworking references include mm-to-fraction conversion charts.

Is 10mm the same as 1 centimeter?

Yes, exactly. 10 millimeters = 1 centimeter. The millimeter is one-tenth of a centimeter and one-thousandth of a meter.

Millimeters to Inches Converter

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