Mm to Inches Converter — With Fractions to 1/64 Inch

How to convert millimeters to inches

Divide the millimeters by 25.4:

inches = millimeters ÷ 25.4

10 mm ÷ 25.4 = 0.3937 in. Tools and hardware in the U.S. are marked in fractions, so the converter also gives the nearest 1/64 inch: 10 mm ≈ 25/64 in. Sixty-fourths are the steps of a standard fractional drill set; a sixteenth (about 1.6 mm) is too coarse for small parts.

For the other direction, multiply inches by 25.4 — the inches to millimeters converter takes fractions like 3/8. For centimeters, use cm to inches.

Millimeters to inches chart with fractions

mm	Inches	Nearest 1/16 in	Nearest 1/64 in
1 mm	0.0394 in	1/16	3/64
2 mm	0.0787 in	1/16	5/64
3 mm	0.1181 in	1/8	1/8
4 mm	0.1575 in	3/16	5/32
5 mm	0.1969 in	3/16	13/64
6 mm	0.2362 in	1/4	15/64
8 mm	0.315 in	5/16	5/16
10 mm	0.3937 in	3/8	25/64
12 mm	0.4724 in	1/2	15/32
13 mm	0.5118 in	1/2	33/64
15 mm	0.5906 in	9/16	19/32
16 mm	0.6299 in	5/8	5/8
19 mm	0.748 in	3/4	3/4
20 mm	0.7874 in	13/16	25/32
22 mm	0.8661 in	7/8	55/64
25 mm	0.9843 in	1	63/64
50 mm	1.969 in	1 15/16	1 31/32
100 mm	3.937 in	3 15/16	3 15/16

To convert a parts list, open Convert a list of values, paste the millimeters one per line and download the inches as CSV.

Metric and inch tools are not interchangeable

The nearest fraction is rarely exact. A 13 mm socket is 0.3 mm bigger than 1/2 in (12.7 mm); a 6 mm drill is 0.35 mm smaller than 1/4 in. For a loose fit — a clearance hole, a shelf pin — the nearest fraction may do. For a wrench on a bolt head or a tight-fitting dowel, use the size the part was made in. The Exact line shows how far apart the two are.

Millimeters, centimeters and inches

Ten millimeters make a centimeter, so 25.4 mm is 2.54 cm — the same inch. Rulers marked in both units show it: 1 inch lines up with 2.54 on the metric side. For sizes already in centimeters, use inches to centimeters or its reverse; to move between millimeters and centimeters, see cm to mm.

Rainfall in millimeters and inches

Weather services outside the U.S. report rain in millimeters; the National Weather Service uses inches.

Rain	Inches
1 mm	0.04 in
5 mm	0.2 in
10 mm	0.39 in
25 mm	0.98 in
50 mm	1.97 in
100 mm	3.94 in

A millimeter of rain means a layer 1 mm deep over flat ground — one liter of water on every square meter.

Frequently asked questions

How many inches is 1 mm?

0.03937 inch. An inch is exactly 25.4 mm, so a millimeter is 1 ÷ 25.4 = 0.0393700787 inch — a bit more than 1/32 inch (3/64 to the nearest sixty-fourth).

What is 10 mm in inches?

0.3937 inch, or 25/64 inch to the nearest sixty-fourth — just over 3/8 inch (0.375 in).

What fraction of an inch is 6 mm?

About 15/64 inch (0.2362 in). The nearest sixteenth is 1/4 inch, which is 6.35 mm — 0.35 mm bigger.

Is 13 mm the same as 1/2 inch?

No. 1/2 inch is 12.7 mm, so a 13 mm wrench or socket is 0.3 mm larger. It may slip on a 1/2-inch bolt head; use the matching tool where you can.

How many inches of rain is 25 mm?

0.98 inch — almost exactly an inch (25.4 mm). 10 mm of rain is 0.39 inch and 50 mm is 1.97 inches.

What is the easiest way to convert mm to inches in my head?

Divide by 25, then take off a little: 100 mm ÷ 25 = 4 in, minus 1.6% is 3.94 in (exact: 3.937). Dividing by 25 alone is 1.6% high.