A millimeter (mm) is one thousandth of a meter. To convert mm to inches, divide by 25.4, because 1 inch is defined as exactly 25.4 mm.
1 inch = 25.4 mm
Exactly, by definition · 1 mm ≈ 0.03937 in · inches = millimeters ÷ 25.4
- Inches
- ≈ 0.3937 in
- Nearest 1/16″
- 3/8″ 10 mm is 0.48 mm longer
- Nearest 1/32″
- 13/32″ 10 mm is 0.32 mm shorter
- Nearest 1/64″
- 25/64″ 10 mm is 0.08 mm longer
What is an mm to inches converter?
An mm to inches converter turns a length in millimeters into inches. This one shows the decimal value and the nearest 1/16, 1/32 and 1/64 inch fraction, and says whether your length is slightly more or slightly less than that fraction. That matters when you are reading a tape measure, a ruler or a drill bit chart.
How to convert mm to inches
- Take the length in millimeters.
- Divide it by 25.4.
- The result is the length in inches. Round it to the precision you need.
- For a tape measure, find the nearest fraction (1/16, 1/32 or 1/64) and check whether your length is a little more or less than it.
Formula: inches = millimeters ÷ 25.4
Worked example: 8 mm ÷ 25.4 = 0.31496… in, which rounds to ≈ 0.315 in. The nearest 1/16 inch is 5/16″ (0.3125 in), and 8 mm is about 0.06 mm longer than that.
To go the other way, multiply inches by 25.4. For example, 1/2 inch × 25.4 = 12.7 mm exactly.
No calculator? Dividing by 25 gives a quick estimate that is about 1.6% too high.
MM to inches chart (1 to 100 mm)
Every millimeter from 1 to 100 with its decimal inches and nearest 1/16 and 1/32 inch fraction. Print it or download the PDF for your workshop wall.
Decimals are rounded to 3 places. In the fraction columns, + means the value is slightly longer than the fraction, − slightly shorter, and = exact.
| Millimeters (mm) | Inches (decimal) | Nearest 1/16″ | Nearest 1/32″ |
|---|---|---|---|
| 1 mm | 0.039 | 1/16″ − | 1/32″ + |
| 2 mm | 0.079 | 1/16″ + | 3/32″ − |
| 3 mm | 0.118 | 1/8″ − | 1/8″ − |
| 4 mm | 0.157 | 3/16″ − | 5/32″ + |
| 5 mm | 0.197 | 3/16″ + | 3/16″ + |
| 6 mm | 0.236 | 1/4″ − | 1/4″ − |
| 7 mm | 0.276 | 1/4″ + | 9/32″ − |
| 8 mm | 0.315 | 5/16″ + | 5/16″ + |
| 9 mm | 0.354 | 3/8″ − | 11/32″ + |
| 10 mm | 0.394 | 3/8″ + | 13/32″ − |
| 11 mm | 0.433 | 7/16″ − | 7/16″ − |
| 12 mm | 0.472 | 1/2″ − | 15/32″ + |
| 13 mm | 0.512 | 1/2″ + | 1/2″ + |
| 14 mm | 0.551 | 9/16″ − | 9/16″ − |
| 15 mm | 0.591 | 9/16″ + | 19/32″ − |
| 16 mm | 0.63 | 5/8″ + | 5/8″ + |
| 17 mm | 0.669 | 11/16″ − | 21/32″ + |
| 18 mm | 0.709 | 11/16″ + | 23/32″ − |
| 19 mm | 0.748 | 3/4″ − | 3/4″ − |
| 20 mm | 0.787 | 13/16″ − | 25/32″ + |
| 21 mm | 0.827 | 13/16″ + | 13/16″ + |
| 22 mm | 0.866 | 7/8″ − | 7/8″ − |
| 23 mm | 0.906 | 7/8″ + | 29/32″ − |
| 24 mm | 0.945 | 15/16″ + | 15/16″ + |
| 25 mm | 0.984 | 1″ − | 31/32″ + |
| 26 mm | 1.024 | 1″ + | 1 1/32″ − |
| 27 mm | 1.063 | 1 1/16″ + | 1 1/16″ + |
| 28 mm | 1.102 | 1 1/8″ − | 1 3/32″ + |
| 29 mm | 1.142 | 1 1/8″ + | 1 5/32″ − |
| 30 mm | 1.181 | 1 3/16″ − | 1 3/16″ − |
| 31 mm | 1.22 | 1 1/4″ − | 1 7/32″ + |
| 32 mm | 1.26 | 1 1/4″ + | 1 1/4″ + |
| 33 mm | 1.299 | 1 5/16″ − | 1 5/16″ − |
| 34 mm | 1.339 | 1 5/16″ + | 1 11/32″ − |
| 35 mm | 1.378 | 1 3/8″ + | 1 3/8″ + |
| 36 mm | 1.417 | 1 7/16″ − | 1 13/32″ + |
| 37 mm | 1.457 | 1 7/16″ + | 1 15/32″ − |
| 38 mm | 1.496 | 1 1/2″ − | 1 1/2″ − |
| 39 mm | 1.535 | 1 9/16″ − | 1 17/32″ + |
| 40 mm | 1.575 | 1 9/16″ + | 1 9/16″ + |
| 41 mm | 1.614 | 1 5/8″ − | 1 5/8″ − |
| 42 mm | 1.654 | 1 5/8″ + | 1 21/32″ − |
| 43 mm | 1.693 | 1 11/16″ + | 1 11/16″ + |
| 44 mm | 1.732 | 1 3/4″ − | 1 23/32″ + |
| 45 mm | 1.772 | 1 3/4″ + | 1 25/32″ − |
| 46 mm | 1.811 | 1 13/16″ − | 1 13/16″ − |
| 47 mm | 1.85 | 1 7/8″ − | 1 27/32″ + |
| 48 mm | 1.89 | 1 7/8″ + | 1 7/8″ + |
| 49 mm | 1.929 | 1 15/16″ − | 1 15/16″ − |
| 50 mm | 1.969 | 1 15/16″ + | 1 31/32″ − |
| 51 mm | 2.008 | 2″ + | 2″ + |
| 52 mm | 2.047 | 2 1/16″ − | 2 1/16″ − |
| 53 mm | 2.087 | 2 1/16″ + | 2 3/32″ − |
| 54 mm | 2.126 | 2 1/8″ + | 2 1/8″ + |
| 55 mm | 2.165 | 2 3/16″ − | 2 5/32″ + |
| 56 mm | 2.205 | 2 3/16″ + | 2 7/32″ − |
| 57 mm | 2.244 | 2 1/4″ − | 2 1/4″ − |
| 58 mm | 2.283 | 2 5/16″ − | 2 9/32″ + |
| 59 mm | 2.323 | 2 5/16″ + | 2 5/16″ + |
| 60 mm | 2.362 | 2 3/8″ − | 2 3/8″ − |
| 61 mm | 2.402 | 2 3/8″ + | 2 13/32″ − |
| 62 mm | 2.441 | 2 7/16″ + | 2 7/16″ + |
| 63 mm | 2.48 | 2 1/2″ − | 2 15/32″ + |
| 64 mm | 2.52 | 2 1/2″ + | 2 17/32″ − |
| 65 mm | 2.559 | 2 9/16″ − | 2 9/16″ − |
| 66 mm | 2.598 | 2 5/8″ − | 2 19/32″ + |
| 67 mm | 2.638 | 2 5/8″ + | 2 5/8″ + |
| 68 mm | 2.677 | 2 11/16″ − | 2 11/16″ − |
| 69 mm | 2.717 | 2 11/16″ + | 2 23/32″ − |
| 70 mm | 2.756 | 2 3/4″ + | 2 3/4″ + |
| 71 mm | 2.795 | 2 13/16″ − | 2 25/32″ + |
| 72 mm | 2.835 | 2 13/16″ + | 2 27/32″ − |
| 73 mm | 2.874 | 2 7/8″ − | 2 7/8″ − |
| 74 mm | 2.913 | 2 15/16″ − | 2 29/32″ + |
| 75 mm | 2.953 | 2 15/16″ + | 2 15/16″ + |
| 76 mm | 2.992 | 3″ − | 3″ − |
| 77 mm | 3.031 | 3 1/16″ − | 3 1/32″ + |
| 78 mm | 3.071 | 3 1/16″ + | 3 1/16″ + |
| 79 mm | 3.11 | 3 1/8″ − | 3 1/8″ − |
| 80 mm | 3.15 | 3 1/8″ + | 3 5/32″ − |
| 81 mm | 3.189 | 3 3/16″ + | 3 3/16″ + |
| 82 mm | 3.228 | 3 1/4″ − | 3 7/32″ + |
| 83 mm | 3.268 | 3 1/4″ + | 3 9/32″ − |
| 84 mm | 3.307 | 3 5/16″ − | 3 5/16″ − |
| 85 mm | 3.346 | 3 3/8″ − | 3 11/32″ + |
| 86 mm | 3.386 | 3 3/8″ + | 3 3/8″ + |
| 87 mm | 3.425 | 3 7/16″ − | 3 7/16″ − |
| 88 mm | 3.465 | 3 7/16″ + | 3 15/32″ − |
| 89 mm | 3.504 | 3 1/2″ + | 3 1/2″ + |
| 90 mm | 3.543 | 3 9/16″ − | 3 17/32″ + |
| 91 mm | 3.583 | 3 9/16″ + | 3 19/32″ − |
| 92 mm | 3.622 | 3 5/8″ − | 3 5/8″ − |
| 93 mm | 3.661 | 3 11/16″ − | 3 21/32″ + |
| 94 mm | 3.701 | 3 11/16″ + | 3 11/16″ + |
| 95 mm | 3.74 | 3 3/4″ − | 3 3/4″ − |
| 96 mm | 3.78 | 3 3/4″ + | 3 25/32″ − |
| 97 mm | 3.819 | 3 13/16″ + | 3 13/16″ + |
| 98 mm | 3.858 | 3 7/8″ − | 3 27/32″ + |
| 99 mm | 3.898 | 3 7/8″ + | 3 29/32″ − |
| 100 mm | 3.937 | 3 15/16″ − | 3 15/16″ − |
Inch fractions to mm
Going the other direction: common inch fractions in millimeters. These values are exact.
| Inches (in) | Inches (decimal) | Millimeters (mm) |
|---|---|---|
| 1/16″ | 0.0625 | 1.5875 |
| 1/8″ | 0.125 | 3.175 |
| 3/16″ | 0.1875 | 4.7625 |
| 1/4″ | 0.25 | 6.35 |
| 5/16″ | 0.3125 | 7.9375 |
| 3/8″ | 0.375 | 9.525 |
| 7/16″ | 0.4375 | 11.1125 |
| 1/2″ | 0.5 | 12.7 |
| 9/16″ | 0.5625 | 14.2875 |
| 5/8″ | 0.625 | 15.875 |
| 11/16″ | 0.6875 | 17.4625 |
| 3/4″ | 0.75 | 19.05 |
| 13/16″ | 0.8125 | 20.6375 |
| 7/8″ | 0.875 | 22.225 |
| 15/16″ | 0.9375 | 23.8125 |
| 1″ | 1 | 25.4 |
Common sizes in millimeters and inches
Metric sizes show up all over the workshop, the toolbox and the jewelry bench. The nearest fraction is the closest 1/16, 1/32 or 1/64 inch that is within about 0.2 mm. The last column shows how far off it is, so you can see when an inch tool will not be a true fit for a metric size.
Wrench and socket sizes
| Size | Millimeters | Inches (decimal) | Nearest fraction | Difference |
|---|---|---|---|---|
| Socket / wrench | 8 mm | 0.315 | ≈ 5/16″ | 0.06 mm longer |
| Socket / wrench | 10 mm | 0.394 | ≈ 25/64″ | 0.08 mm longer |
| Socket / wrench | 13 mm | 0.512 | ≈ 33/64″ | 0.1 mm shorter |
| Socket / wrench | 17 mm | 0.669 | ≈ 43/64″ | 0.07 mm shorter |
| Socket / wrench | 19 mm | 0.748 | ≈ 3/4″ | 0.05 mm shorter |
| Socket / wrench | 22 mm | 0.866 | ≈ 55/64″ | 0.17 mm longer |
A 13 mm socket is close to 1/2 inch, but 1/2 inch is 12.7 mm, so the two are not interchangeable on a tight fastener.
Drill bit and bolt diameters
| Use | Millimeters | Inches (decimal) | Nearest fraction | Difference |
|---|---|---|---|---|
| Drill bit / M3 bolt | 3 mm | 0.118 | ≈ 1/8″ | 0.18 mm shorter |
| Drill bit / M4 bolt | 4 mm | 0.157 | ≈ 5/32″ | 0.03 mm longer |
| Drill bit / M5 bolt | 5 mm | 0.197 | ≈ 13/64″ | 0.16 mm shorter |
| Drill bit / M6 bolt | 6 mm | 0.236 | ≈ 15/64″ | 0.05 mm longer |
| Drill bit / M8 bolt | 8 mm | 0.315 | ≈ 5/16″ | 0.06 mm longer |
| Drill bit / M10 bolt | 10 mm | 0.394 | ≈ 25/64″ | 0.08 mm longer |
Metric and inch drill bits are not the same sizes. For a clean fit, choose the exact bit size the fastener calls for.
Bead and jewelry sizes
| Item | Millimeters | Inches (decimal) | Nearest fraction | Difference |
|---|---|---|---|---|
| Bead | 4 mm | 0.157 | ≈ 5/32″ | 0.03 mm longer |
| Bead | 6 mm | 0.236 | ≈ 15/64″ | 0.05 mm longer |
| Bead | 8 mm | 0.315 | ≈ 5/16″ | 0.06 mm longer |
| Bead | 10 mm | 0.394 | ≈ 25/64″ | 0.08 mm longer |
| Bead | 12 mm | 0.472 | ≈ 15/32″ | 0.09 mm longer |
Film and audio plugs
| Item | Millimeters | Inches (decimal) | Nearest fraction | Difference |
|---|---|---|---|---|
| Audio plug | 2.5 mm | 0.098 | ≈ 3/32″ | 0.12 mm longer |
| Audio plug | 3.5 mm | 0.138 | ≈ 9/64″ | 0.07 mm shorter |
| Film width | 8 mm | 0.315 | ≈ 5/16″ | 0.06 mm longer |
| Film width | 16 mm | 0.63 | ≈ 5/8″ | 0.13 mm longer |
| Film width | 35 mm | 1.378 | ≈ 1 3/8″ | 0.08 mm longer |
Frequently asked questions
How many inches is 1 mm?
1 mm is exactly 1/25.4 inch, which is about 0.0394 inch. Because the result does not end, it is written with the approximately-equal sign.
How many mm are in an inch?
There are exactly 25.4 mm in 1 inch. This is a definition, not a rounded value.
What is 8 mm in inches?
8 mm is about 0.315 inch. The nearest 1/16 inch is 5/16 inch, and 8 mm is slightly longer than that, by about 0.06 mm.
What is 10 mm in inches?
10 mm is about 0.394 inch. The nearest 1/16 inch is 3/8 inch (10 mm is about 0.48 mm longer), and the nearest 1/32 inch is 13/32 inch (10 mm is about 0.32 mm shorter).
What is 25 mm in inches?
25 mm is about 0.984 inch, just under 1 inch. A full inch is 25.4 mm, so 25 mm is 0.4 mm short of an inch.
How do I convert mm to inches without a calculator?
Divide the millimeters by 25 for a quick estimate. It is about 1.6% too high, because the exact divisor is 25.4. For exact work, divide by 25.4.
Is 1 inch exactly 25.4 mm?
Yes. The inch has been defined as exactly 25.4 mm since the international yard and pound agreement of 1959, and NIST lists the factor as exact.
What does the ≈ sign mean in these results?
It means the value is rounded. An equals sign is used only when the result is exact, such as 50.8 mm = 2 inches.