Millimeters to Inches (mm to in)
1 mm = 0.0393701 in
To convert millimeters to inches: inches = millimeters ÷ 25.4
| millimeters | inches |
|---|---|
| 1 mm | 0.03937 in |
| 2 mm | 0.07874 in |
| 3 mm | 0.1181 in |
| 4 mm | 0.1575 in |
| 5 mm | 0.1969 in |
| 6 mm | 0.2362 in |
| 8 mm | 0.315 in |
| 10 mm | 0.3937 in |
Divide millimeters by 25.4 to get inches — an inch is exactly 25.4 mm. One millimeter is about 0.0394 inches, a little over 1/32 inch.
Formula
inches = millimeters ÷ 25.4
Example: 4 millimeters = 0.15748 inches.
How to convert millimeters to inches in your head
- Divide by 25 and take off 2%: 50 mm ÷ 25 = 2, minus 0.04 = 1.96 in (exact: 1.9685).
- Four millimeters is just over 5/32 in, and every 25.4 mm is one inch: 76 mm is about 3 in (exact 2.99).
- Rough fractions: 3 mm ≈ 1/8 in, 6 mm ≈ 1/4 in, 10 mm ≈ 3/8 in (a little over), 13 mm ≈ 1/2 in, 19 mm ≈ 3/4 in.
Millimeters to Inches chart
| millimeters | inches |
|---|---|
| 1 | 0.0393701 |
| 2 | 0.0787402 |
| 3 | 0.11811 |
| 4 | 0.15748 |
| 5 | 0.19685 |
| 6 | 0.23622 |
| 8 | 0.314961 |
| 10 | 0.393701 |
| 12 | 0.472441 |
| 13 | 0.511811 |
| 15 | 0.590551 |
| 16 | 0.629921 |
| 19 | 0.748031 |
| 20 | 0.787402 |
| 25 | 0.984252 |
| 30 | 1.1811 |
| 50 | 1.9685 |
| 100 | 3.93701 |
Millimeters to inches with the nearest 1/64 inch fraction
The fraction column rounds to the nearest 1/64 in; "≈" marks values that are not an exact fraction.
| What | millimeters | inches | Nearest fraction |
|---|---|---|---|
| 1 | 0.0393701 | ≈ 3/64 in | |
| 3 | 0.11811 | ≈ 1/8 in | |
| 5 | 0.19685 | ≈ 13/64 in | |
| 6 | 0.23622 | ≈ 15/64 in | |
| 8 | 0.314961 | ≈ 5/16 in | |
| 10 mm (common socket and bolt head) | 10 | 0.393701 | ≈ 25/64 in |
| 12 | 0.472441 | ≈ 15/32 in | |
| 13 | 0.511811 | ≈ 33/64 in | |
| 16 | 0.629921 | ≈ 5/8 in | |
| 19 | 0.748031 | ≈ 3/4 in | |
| 20 | 0.787402 | ≈ 25/32 in | |
| 22 | 0.866142 | ≈ 55/64 in | |
| 25 mm (about one inch of rain) | 25 | 0.984252 | ≈ 63/64 in |
| 32 | 1.25984 | ≈ 1 17/64 in | |
| 50 | 1.9685 | ≈ 1 31/32 in | |
| 100 | 3.93701 | ≈ 3 15/16 in | |
| 300 mm (about one foot) | 300 | 11.811 | ≈ 11 13/16 in |
Good to know
Workshop sizes: 6 mm ≈ 0.236 in (just under 1/4 in, which is 6.35 mm), 10 mm = 0.394 in, 13 mm ≈ 0.512 in (close to 1/2 in, 12.7 mm). Metric and imperial sockets and drill bits are close but not interchangeable at larger sizes.
Rainfall and snowfall: 25 mm of rain is just under an inch.
Read next: Fractional inches to mm: drill bit, wrench and socket size chart
Common millimeters to inches mistakes
- Mixing up mm and cm. 10 mm is 1 cm, so 10 mm is 0.39 in, not 3.9 in.
- Treating a near fraction as exact. 13 mm is 0.512 in, 0.012 in more than 1/2 in; a 13 mm wrench is loose on a 1/2 in nut only slightly, but a 1/2 in bit will not make a 13 mm hole.
- Dividing by 25 for long lengths. 300 mm ÷ 25 = 12 in, but the exact value is 11.81 in, 0.19 in short of a foot.
- Rounding twice. Convert from the original millimeters with ÷ 25.4 (exact since 1959, NIST), then round once at the end.
Sources
Frequently asked questions
How many inches is 1 mm?
0.03937 inches.
How many inches is 10 mm?
10 mm is 0.3937 inches — about 25/64 in.
How many mm is 1/4 inch?
1/4 inch is 6.35 mm.
How many inches is 5 mm?
5 mm is 0.19685 in, about 13/64 in.
How many inches is 8 mm?
8 mm is 0.31496 in, about 5/16 in.
How many inches is 12 mm?
12 mm is 0.47244 in, about 15/32 in.
How many inches is 20 mm?
20 mm is 0.7874 in, about 25/32 in.
How many inches is 25 mm?
25 mm is 0.98425 in, just under 1 in.
How many inches is 50 mm?
50 mm is 1.9685 in, just under 2 in.
How many inches is 100 mm?
100 mm is 3.937 in.