About this tool
This converter uses the exact international standard: 1 inch equals exactly 25.4 millimeters. It divides millimeters by 25.4, or multiplies inches by 25.4, and rounds the answer to at most four decimal places, which is finer than a thousandth of an inch.
How to use the converter
- Type a size into the Millimeters box; decimals such as 1.75 work.
- Read the decimal result in the Inches box, which updates as you type.
- To convert the other way, type into Inches as a decimal (0.375 rather than 3/8) and read Millimeters.
- For the nearest tape-measure fraction, find the size in the fraction chart further down the page.
Worked example
A shelf plan calls for 19 mm plywood. Type 19 into Millimeters and the Inches box shows 0.748, because 19 / 25.4 = 0.74803… rounded to four decimals. The fraction chart lists 19 mm next to 3/4 in with an error of +0.0020 in, so 3/4-inch stock is 0.05 mm thicker. Going the other way, typing 0.375 (3/8 in) into Inches gives 9.525 mm.
Common use cases
- Converting an engineering drawing or parts spec listed in millimeters
- Checking screw, bolt, or hardware sizes between metric and imperial systems
- Converting a small precise measurement, like a phone or watch dimension
Things to watch out for
The 25.4 mm-per-inch figure is an exact international definition, not a rounded approximation — small differences between calculators usually come from how many decimal places the result is rounded to. Because millimeters are a small unit, precision matters more here than in the cm-to-inches conversion — use enough decimal places for parts or fittings where a small error could cause a fit problem.
Common millimeters to inches values
Use this chart when you only need a quick reading. Values are rounded to four decimal places.
| Millimeters | Inches |
|---|---|
| 1 mm | 0.0394 in |
| 2 mm | 0.0787 in |
| 3 mm | 0.1181 in |
| 5 mm | 0.1969 in |
| 6 mm | 0.2362 in |
| 8 mm | 0.3150 in |
| 10 mm | 0.3937 in |
| 12 mm | 0.4724 in |
| 16 mm | 0.6299 in |
| 20 mm | 0.7874 in |
| 25.4 mm | 1.0000 in |
| 30 mm | 1.1811 in |
| 50 mm | 1.9685 in |
| 75 mm | 2.9528 in |
| 100 mm | 3.9370 in |
| 150 mm | 5.9055 in |
How to convert mm to inches by hand
Divide the millimeters by 25.4. For example, 50 mm / 25.4 = 1.9685 inches. To go the other way, multiply inches by 25.4, so 2 inches is 50.8 mm. If you do not have a calculator, a rough shortcut is to divide by 25 and subtract about 1.5%, which gets you close enough for a quick estimate.
Fractions of an inch are common in the workshop. Three millimeters is a little under 1/8 inch (0.118 in against 0.125 in), 6 mm is a little under 1/4 inch (0.236 in against 0.250 in) and 12 mm is a little under 1/2 inch (0.472 in against 0.500 in). The gaps are small but they matter when two parts must fit together, so convert to decimals rather than rounding to the nearest fraction when precision counts.
Where millimeters show up in everyday life
Millimeters are the standard unit for small parts and thin things: drill bits and wrenches, camera lens focal lengths, phone and laptop thickness, rainfall, jewelry sizes and 3D printer filament. A common 1.75 mm filament is 0.069 inches thick, and a 6 mm drill bit is about 0.236 inches wide. US products often list the same dimension in inches, so being able to move between the two avoids buying the wrong size.
MM to inches fraction chart
Every millimeter from 1 to 50 mm, plus common sizes up to 100 mm, shown as decimal inches and as the nearest fraction on a standard 1/16-inch tape measure or ruler. The error columns show how far that fraction is from the true size — useful when deciding whether a fractional drill bit, wrench, or cut is close enough.
| Millimeters | Inches (decimal) | Nearest 1/16 in | Error (in) | Error (mm) |
|---|---|---|---|---|
| 1 mm | 0.0394 | 1/16 | +0.0231 | +0.5875 |
| 2 mm | 0.0787 | 1/16 | −0.0162 | −0.4125 |
| 3 mm | 0.1181 | 1/8 | +0.0069 | +0.1750 |
| 4 mm | 0.1575 | 3/16 | +0.0300 | +0.7625 |
| 5 mm | 0.1969 | 3/16 | −0.0094 | −0.2375 |
| 6 mm | 0.2362 | 1/4 | +0.0138 | +0.3500 |
| 7 mm | 0.2756 | 1/4 | −0.0256 | −0.6500 |
| 8 mm | 0.3150 | 5/16 | −0.0025 | −0.0625 |
| 9 mm | 0.3543 | 3/8 | +0.0207 | +0.5250 |
| 10 mm | 0.3937 | 3/8 | −0.0187 | −0.4750 |
| 11 mm | 0.4331 | 7/16 | +0.0044 | +0.1125 |
| 12 mm | 0.4724 | 1/2 | +0.0276 | +0.7000 |
| 13 mm | 0.5118 | 1/2 | −0.0118 | −0.3000 |
| 14 mm | 0.5512 | 9/16 | +0.0113 | +0.2875 |
| 15 mm | 0.5906 | 9/16 | −0.0281 | −0.7125 |
| 16 mm | 0.6299 | 5/8 | −0.0049 | −0.1250 |
| 17 mm | 0.6693 | 11/16 | +0.0182 | +0.4625 |
| 18 mm | 0.7087 | 11/16 | −0.0212 | −0.5375 |
| 19 mm | 0.7480 | 3/4 | +0.0020 | +0.0500 |
| 20 mm | 0.7874 | 13/16 | +0.0251 | +0.6375 |
| 21 mm | 0.8268 | 13/16 | −0.0143 | −0.3625 |
| 22 mm | 0.8661 | 7/8 | +0.0089 | +0.2250 |
| 23 mm | 0.9055 | 7/8 | −0.0305 | −0.7750 |
| 24 mm | 0.9449 | 15/16 | −0.0074 | −0.1875 |
| 25 mm | 0.9843 | 1 | +0.0157 | +0.4000 |
| 26 mm | 1.0236 | 1 | −0.0236 | −0.6000 |
| 27 mm | 1.0630 | 1 1/16 | −0.0005 | −0.0125 |
| 28 mm | 1.1024 | 1 1/8 | +0.0226 | +0.5750 |
| 29 mm | 1.1417 | 1 1/8 | −0.0167 | −0.4250 |
| 30 mm | 1.1811 | 1 3/16 | +0.0064 | +0.1625 |
| 31 mm | 1.2205 | 1 1/4 | +0.0295 | +0.7500 |
| 32 mm | 1.2598 | 1 1/4 | −0.0098 | −0.2500 |
| 33 mm | 1.2992 | 1 5/16 | +0.0133 | +0.3375 |
| 34 mm | 1.3386 | 1 5/16 | −0.0261 | −0.6625 |
| 35 mm | 1.3780 | 1 3/8 | −0.0030 | −0.0750 |
| 36 mm | 1.4173 | 1 7/16 | +0.0202 | +0.5125 |
| 37 mm | 1.4567 | 1 7/16 | −0.0192 | −0.4875 |
| 38 mm | 1.4961 | 1 1/2 | +0.0039 | +0.1000 |
| 39 mm | 1.5354 | 1 9/16 | +0.0271 | +0.6875 |
| 40 mm | 1.5748 | 1 9/16 | −0.0123 | −0.3125 |
| 41 mm | 1.6142 | 1 5/8 | +0.0108 | +0.2750 |
| 42 mm | 1.6535 | 1 5/8 | −0.0285 | −0.7250 |
| 43 mm | 1.6929 | 1 11/16 | −0.0054 | −0.1375 |
| 44 mm | 1.7323 | 1 3/4 | +0.0177 | +0.4500 |
| 45 mm | 1.7717 | 1 3/4 | −0.0217 | −0.5500 |
| 46 mm | 1.8110 | 1 13/16 | +0.0015 | +0.0375 |
| 47 mm | 1.8504 | 1 7/8 | +0.0246 | +0.6250 |
| 48 mm | 1.8898 | 1 7/8 | −0.0148 | −0.3750 |
| 49 mm | 1.9291 | 1 15/16 | +0.0084 | +0.2125 |
| 50 mm | 1.9685 | 1 15/16 | −0.0310 | −0.7875 |
| 55 mm | 2.1654 | 2 3/16 | +0.0221 | +0.5625 |
| 60 mm | 2.3622 | 2 3/8 | +0.0128 | +0.3250 |
| 65 mm | 2.5591 | 2 9/16 | +0.0034 | +0.0875 |
| 70 mm | 2.7559 | 2 3/4 | −0.0059 | −0.1500 |
| 75 mm | 2.9528 | 2 15/16 | −0.0153 | −0.3875 |
| 80 mm | 3.1496 | 3 1/8 | −0.0246 | −0.6250 |
| 85 mm | 3.3465 | 3 3/8 | +0.0285 | +0.7250 |
| 90 mm | 3.5433 | 3 9/16 | +0.0192 | +0.4875 |
| 95 mm | 3.7402 | 3 3/4 | +0.0098 | +0.2500 |
| 100 mm | 3.9370 | 3 15/16 | +0.0005 | +0.0125 |
Fractional inches to mm
| Fraction | Inches (decimal) | Millimeters |
|---|---|---|
| 1/16 in | 0.0625 | 1.5875 |
| 1/8 in | 0.125 | 3.175 |
| 3/16 in | 0.1875 | 4.7625 |
| 1/4 in | 0.25 | 6.35 |
| 5/16 in | 0.3125 | 7.9375 |
| 3/8 in | 0.375 | 9.525 |
| 7/16 in | 0.4375 | 11.1125 |
| 1/2 in | 0.5 | 12.7 |
| 9/16 in | 0.5625 | 14.2875 |
| 5/8 in | 0.625 | 15.875 |
| 11/16 in | 0.6875 | 17.4625 |
| 3/4 in | 0.75 | 19.05 |
| 13/16 in | 0.8125 | 20.6375 |
| 7/8 in | 0.875 | 22.225 |
| 15/16 in | 0.9375 | 23.8125 |
| 1 in | 1 | 25.4 |
Source: thealltools.com/tools/mm-to-inches
Frequently asked questions
1 millimeter equals 0.03937 inches. Since 1 inch is exactly 25.4 mm, 1 mm is exactly 1 ÷ 25.4 inches.
Same underlying math, different unit of length — a millimeter is one-tenth of a centimeter, so this tool is useful when your starting measurement is already in mm, like on an engineering drawing or a small parts spec.
Millimeters give finer precision than inches without needing fractions — instead of writing 1/64 inch, a measurement can be written as a clean decimal like 0.4 mm, which is why many international manufacturing and engineering specs default to millimeters.
Divide the millimeters by 25.4 to get decimal inches, multiply by 16, round to the nearest whole number, and put it over 16 (then reduce). For example, 10 mm = 0.3937 in; 0.3937 × 16 ≈ 6.3, which rounds to 6/16 = 3/8 in (0.375 in, about 0.0187 in smaller than 10 mm).