Length conversion

Millimetres to Inches (mm to in)

Compare a measured thickness or part dimension with an inch-based drawing. A converted measurement does not identify a nominal pipe size or a compatible thread.

1 mm ≈ 0.0394 in — the calculator keeps the stored factor; this summary may be rounded.

millimetres

inches

All units & categories

Sheet material measured as 3 mm thick

Starting measurement: 3 mm
Converted value (rounded if needed): 0.1181 in

Keep the drawing’s tolerance alongside the converted thickness. Rounding to the nearest familiar fraction can conceal a difference that matters for a fitted part.

Millimetres to Inches conversion chart

millimetres to inches. Values are calculated from the stored unit factors and rounded for this chart.
millimetres	inches
1 mm	0.0394 in
2 mm	0.0787 in
3 mm	0.1181 in
4 mm	0.1575 in
5 mm	0.1968 in
6 mm	0.2362 in
7 mm	0.2756 in
8 mm	0.315 in
9 mm	0.3543 in
10 mm	0.3937 in
12 mm	0.4724 in
15 mm	0.5906 in
18 mm	0.7087 in
20 mm	0.7874 in
25 mm	0.9843 in
30 mm	1.1811 in
40 mm	1.5748 in
50 mm	1.9685 in
60 mm	2.3622 in
75 mm	2.9528 in
100 mm	3.937 in

How to convert by hand

Reference relationship (display may be rounded)

1 mm = 0.0393700787 in

Multiply the amount in millimetres by the number of inches per unit.
Use the calculator for the stored precision; copying a short displayed factor introduces extra rounding.
Round the result to suit your measurement, after completing the calculation.

Related conversions

About millimetres and inches

Convert each measured dimension separately. A width stays a width and a diagonal stays a diagonal; changing units does not turn a product’s nominal size into a measured size.

Millimetre

Metric (SI)

One thousandth of a metre. Small differences matter when checking a part against a drawing.

Commonly used for: Material thickness, fastener dimensions and workshop measurements.

Inch

US / Imperial

Exactly 2.54 centimetres under the 1959 international yard agreement. The symbol is in; a double-prime mark is also used on drawings.

Commonly used for: Screen diagonals, picture sizes and dimensions on US product listings.

Questions

Is a nearby fractional inch size an exact replacement?

Not necessarily. A metric dimension and the nearest common inch fraction can be close without matching. Check the actual dimensions and allowed tolerance before choosing a replacement part.

How do I convert inches back to millimetres?

Enter the value in the inches field above to work backwards, or open the Inches to Millimetres converter. This uses the stored factors rather than dividing by a rounded number copied from the chart.

Why might the chart and calculator show different decimal places?

The chart uses a compact rounded display. The editable calculator can show up to six decimal places and uses the factors or temperature formulas stored in the library. More displayed digits do not make the original measurement more precise.

Precision and source

The calculator uses stored conversion factors and temperature formulas, then rounds the result for display. A short decimal in a chart is not a claim of exactness. For a calculation with several steps, keep as much precision as the original measurement supports and round at the end.

Reference: NIST SP 811 conversion factors. Its alphabetical tables distinguish unit variants and temperature readings from intervals. Published by ToolsNow. Report a conversion problem.

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