Unit converter

Millimeters to Inches (mm to in)

Divide millimeters by 25.4 to get inches, since one inch is exactly 25.4 mm. 10 mm is 0.394 in, a hair over 3/8 in. The table also rounds each value to the nearest 1/32 of an inch, the finest mark on most tape measures and rulers.

Convert mm to inches

mm to inches

10 mm = 0.393701 in

1 mm = 0.0393701 in · 1 in = 25.4 mm

Show the math

in = mm ÷ 25.4

Uses exact legal definitions; results are rounded to 6 significant figures for display.

How to convert mm to inches

in = mm ÷ 25.4

One inch is exactly 25.4 millimeters, so divide by 25.4. If you'd rather multiply, use 0.0393701 (rounded).

Worked example: converting 10 mm:

in = mm ÷ 25.4
10 mm ÷ 25.4 = 0.393701 in

Mm to inches conversion table

Common values, each computed with the exact formula and rounded to 6 significant figures.

Millimeters (mm) to Inches (in)
Millimeters (mm)	Inches (in)	Nearest 1/32 in
0.5 mm	0.019685 in	1/32 in
1 mm	0.0393701 in	1/32 in
1.5 mm	0.0590551 in	1/16 in
1.75 mm	0.0688976 in	1/16 in
2 mm	0.0787402 in	3/32 in
2.5 mm	0.0984252 in	3/32 in
3 mm	0.11811 in	1/8 in
4 mm	0.15748 in	5/32 in
5 mm	0.19685 in	3/16 in
6 mm	0.23622 in	1/4 in
7 mm	0.275591 in	9/32 in
8 mm	0.314961 in	5/16 in
9 mm	0.354331 in	11/32 in
10 mm	0.393701 in	13/32 in
11 mm	0.433071 in	7/16 in
12 mm	0.472441 in	15/32 in
13 mm	0.511811 in	1/2 in
14 mm	0.551181 in	9/16 in
15 mm	0.590551 in	19/32 in
16 mm	0.629921 in	5/8 in
17 mm	0.669291 in	21/32 in
18 mm	0.708661 in	23/32 in
19 mm	0.748031 in	3/4 in
20 mm	0.787402 in	25/32 in
22 mm	0.866142 in	7/8 in
24 mm	0.944882 in	15/16 in
25 mm	0.984252 in	31/32 in
25.4 mm	1 in	1 in
30 mm	1.1811 in	1 3/16 in
32 mm	1.25984 in	1 1/4 in
35 mm	1.37795 in	1 3/8 in
40 mm	1.5748 in	1 9/16 in
45 mm	1.77165 in	1 25/32 in
50 mm	1.9685 in	1 31/32 in
60 mm	2.3622 in	2 3/8 in
75 mm	2.95276 in	2 15/16 in
100 mm	3.93701 in	3 15/16 in
150 mm	5.90551 in	5 29/32 in
200 mm	7.87402 in	7 7/8 in
300 mm	11.811 in	11 13/16 in

Quick reference: everyday millimeters in inches

Common 3D-printer filament
1.75 mm = 0.0688976 in
10 mm socket (common on cars)
10 mm = 0.393701 in
19 mm socket (≈ 3/4 in)
19 mm = 0.748031 in
One inch
25.4 mm = 1 in
Heavy daily rainfall
50 mm = 1.9685 in

Metric vs. SAE wrenches, sockets and bolts

Some metric and SAE (inch) wrenches are close enough to swap, and some aren't. A 19 mm socket is 0.748 in, almost identical to 3/4 in (0.750), so the two are interchangeable in practice. A 10 mm wrench is 0.394 in, 0.019 in larger than 3/8 in, and that slop is enough to round off a tight bolt head.

Thread pitch is another trap. Metric bolts are specified by diameter and pitch in millimeters (M8 × 1.25), while inch bolts use threads per inch. A converted diameter that looks close doesn't make a bolt fit, so match the full thread specification, not just the size.

Rainfall, filament, jewelry and other small sizes

Weather services outside the US report rainfall in millimeters. 25.4 mm of rain is one inch, and a 50 mm downpour is just under 2 inches. 3D-printer filament comes in 1.75 mm (0.069 in) and 2.85 mm (0.112 in) diameters, and a printer built for one won't feed the other.

For decimal-inch work such as machining, keep three or four decimal places. For carpentry, the nearest 1/16 or 1/32 inch is the practical limit of a tape measure. If you need to add or subtract the fractions in the table's third column, our fraction calculator works in exact fractions.

Frequently asked questions

What fraction of an inch is 1 mm?

1 mm is 0.03937 in, slightly more than 1/32 in (0.03125) and less than 1/16 in (0.0625). The nearest common fraction is 1/32 in. For a tighter match, 5/127 in is exact, but no tape measure is marked that way. In practice, think of a millimeter as 'a bit more than a thirty-second'.

Can I use a 13 mm socket on a 1/2-inch bolt?

Usually it will turn the bolt, but it isn't a good fit. 13 mm is 0.512 in, 0.012 in larger than 1/2 in, so it may slip under heavy torque, especially with 6-point sockets on worn fasteners. For a stubborn or high-torque bolt, use the correct SAE size. Here 1/2 in is 12.7 mm.

How many mm are in a quarter inch?

A quarter inch is 6.35 mm exactly (25.4 ÷ 4). Many metric tools round that to 6 mm or 6.5 mm, so a 6 mm drill bit makes a slightly smaller hole than a 1/4-inch bit. For the other direction, see the inches to mm converter, which lists common fractions.