Millimeters to Inches Converter

Length conversion · Updated 2026-10-04

Converting millimeters to inches is a multiplication by a fixed factor: 1 mm = 0.03937008 in. The table below covers the values people look up most often, and the formula section shows exactly where that factor comes from.

Because one millimeter works out to 0.03937008 in, the inch is the far smaller unit of the two: a figure given in inch always carries a smaller number than the same measurement in millimeter. A chart drawn in mm can hide that, so check which label the axis uses before you compare two readings.

DIY and home-improvement work is where this pair shows up most: you measure in millimeters but the hardware store or an imported product sheet quotes inches, so the conversion has to be right the first time.

The conversion factor used here is 0.03937008 in per millimeter (8 significant digits as shown). Kept to seven figures it covers professional measurement; if you round it to two or three decimals for a spreadsheet, the error scales with the input — at a value of 1,000 mm a factor rounded to three decimals can be off by a measurable amount. The reverse direction uses 25.4 mm per in, the exact reciprocal, so a round trip through both pages returns your original number.

Millimeters to Inches formula

Use this formula to convert any millimeter value to inches:

Worked example: 100 mm × 0.03937008 = 3.937008 in.

Millimeters to Inches conversion table

Millimeters (mm)	Inches (in)
0.5 mm	0.01968504 in
1 mm	0.03937008 in
2 mm	0.07874016 in
5 mm	0.1968504 in
10 mm	0.3937008 in
20 mm	0.7874016 in
50 mm	1.968504 in
100 mm	3.937008 in
500 mm	19.68504 in
1000 mm	39.37008 in

How to convert millimeters to inches

Multiply the millimeter value by 0.03937008 to get the equivalent in inches. This single factor works for every value in the table above and for anything else you need — there is no per-value adjustment, which is why a conversion table and a calculator always agree.

If you need the opposite direction, use the Inches to Millimeters converter instead of dividing by hand; both pages use the same source factors. For every other mm conversion in one place, see the mm conversion hub.

Frequently asked questions

How many inches are in 1 millimeter?
1 millimeter = 0.03937008 in.

What is 100 millimeters in inches?
100 mm = 3.937008 in.

Is converting millimeters to inches the same as inches to millimeters?
No — the direction changes the multiplier. The reverse conversion (1 in = 25.4 mm) is on the Inches to Millimeters page.

Related conversions

Try the ConvBolt Unit Converter for any other length unit, browse the Length conversions, or read our conversion guides.