Enter any value in millimeters and instantly read the result in decimal inches. The fraction table further down the page also shows the nearest inch fraction used for drill bits and bolts. The converter comes in handy for precise measurements: material thickness, electronic component dimensions, or matching a metric spec to your fractional-inch tools.
The inch rules everyday measurement in the United States, where drill bits, bolts, socket wrenches, and building materials are all sized in inches or inch fractions. The millimeter is the standard unit of precise measurement in Europe and most of the rest of the world. The problem appears when you buy a European product with a metric spec, work on a car that uses metric fasteners, or try to match a millimeter dimension from a manual to your fractional-inch tool set.
One inch is exactly 25.4 mm. This relationship is fixed and applies everywhere, so every conversion comes down to a single division. The converter does it for you the moment you type a value.
Further down the page you will find a mm-to-inches conversion table for values from 1 to 800 mm and a table of the most common inch fractions with their millimeter equivalents.
Converting millimeters to inches relies on one fixed relationship: one inch is exactly 25.4 mm. Simply divide the number of millimeters by 25.4 to get the result in inches.
The full formula: inches = millimeters ÷ 25.4. The other way around: millimeters = inches × 25.4.
Example: you want to know how many inches 14 mm is. Plug it in: 14 ÷ 25.4 = 0.551 inches. That is not exactly 1/2 inch (12.7 mm) or 3/4 inch (19.05 mm) — the nearest common fraction is 9/16 inch (14.29 mm), though the difference is still about 0.29 mm.
Another example: the standard thickness of printed circuit board (PCB) laminate is 1.6 mm, which converts to 1.6 ÷ 25.4 = 0.063 inches — a value close to 1/16 inch (0.0625 inches). The converter handles both directions the moment you type a value.
The table below converts common millimeter values to decimal inches. Values are rounded to three decimal places. To convert an exact value or less common dimensions, use the converter above.
| Millimeters | Inches |
|---|---|
| 1 mm | 0.039 in |
| 2 mm | 0.079 in |
| 3 mm | 0.118 in |
| 4 mm | 0.157 in |
| 5 mm | 0.197 in |
| 6 mm | 0.236 in |
| 7 mm | 0.276 in |
| 8 mm | 0.315 in |
| 9 mm | 0.354 in |
| 10 mm | 0.394 in |
| 12 mm | 0.472 in |
| 14 mm | 0.551 in |
| 15 mm | 0.591 in |
| 16 mm | 0.630 in |
| 18 mm | 0.709 in |
| 20 mm | 0.787 in |
| 25 mm | 0.984 in |
| 30 mm | 1.181 in |
| 35 mm | 1.378 in |
| 40 mm | 1.575 in |
| 50 mm | 1.969 in |
| 60 mm | 2.362 in |
| 70 mm | 2.756 in |
| 80 mm | 3.150 in |
| 90 mm | 3.543 in |
| 100 mm | 3.937 in |
| 120 mm | 4.724 in |
| 150 mm | 5.906 in |
| 180 mm | 7.087 in |
| 200 mm | 7.874 in |
| 210 mm | 8.268 in |
| 250 mm | 9.843 in |
| 256 mm | 10.079 in |
| 297 mm | 11.693 in |
| 300 mm | 11.811 in |
| 500 mm | 19.685 in |
| 800 mm | 31.496 in |
Want to convert the other way? Use our <a href="/en/tools/inches-to-mm-converter">inches to mm</a> converter, which includes a full inch fraction table in 1/32 steps.
Drill bits, bolts, socket wrenches, and construction profiles are sized in inch fractions, not decimal values. The table below shows the most frequently used fractions together with their decimal and millimeter values. Millimeter values are rounded to two decimal places.
| Inch (fraction) | Inch (decimal) | Millimeters |
|---|---|---|
| 1/16 in | 0.0625 in | 1.59 mm |
| 1/8 in | 0.125 in | 3.18 mm |
| 5/32 in | 0.15625 in | 3.97 mm |
| 3/16 in | 0.1875 in | 4.76 mm |
| 1/4 in | 0.25 in | 6.35 mm |
| 5/16 in | 0.3125 in | 7.94 mm |
| 3/8 in | 0.375 in | 9.53 mm |
| 7/16 in | 0.4375 in | 11.11 mm |
| 1/2 in | 0.5 in | 12.70 mm |
| 9/16 in | 0.5625 in | 14.29 mm |
| 5/8 in | 0.625 in | 15.88 mm |
| 11/16 in | 0.6875 in | 17.46 mm |
| 3/4 in | 0.75 in | 19.05 mm |
| 13/16 in | 0.8125 in | 20.64 mm |
| 7/8 in | 0.875 in | 22.23 mm |
| 1 in | 1 in | 25.40 mm |
Converting mm to inches comes up wherever measurement precision matters. Each of the situations below has its own specifics.
100 mm is 3.937 inches. Calculation: 100 ÷ 25.4 = 3.937 in. Rounding up, that is just under 4 inches.
25 mm is 0.984 inches. Calculation: 25 ÷ 25.4 = 0.984 in. That is close to, but not equal to, 1 inch — exactly 1 inch is 25.4 mm, so the difference is 0.4 mm.
10 mm is 0.394 inches. Calculation: 10 ÷ 25.4 = 0.394 in. That is not 1/4 inch (0.25 in = 6.35 mm) — 10 mm corresponds to roughly 25/64 inch.
1 mm = 0.039 in, 2 mm = 0.079 in, 3 mm = 0.118 in, 20 mm = 0.787 in, and 30 mm = 1.181 in. You get each of these values by dividing the number of millimeters by 25.4.
150 mm is 5.906 inches. Calculation: 150 ÷ 25.4 = 5.906 in. That is close to 6 inches, with a difference of about 2.4 mm.
6 mm = 0.236 in, 15 mm = 0.591 in, 40 mm = 1.575 in, 50 mm = 1.969 in, and 180 mm = 7.087 in. All values follow the same rule: divide the millimeters by 25.4.
5 mm is 0.197 inches. Calculation: 5 ÷ 25.4 = 0.197 in. That is close to 3/16 inch (0.1875 in = 4.76 mm).
First convert the millimeters to decimal inches (mm ÷ 25.4), then find the nearest common fraction in the table above. For example, 9 mm = 0.354 in, which is close to 23/64 inch, though in practice you round to the nearest available drill bit or wrench size, usually in 1/32 or 1/16 inch steps.
No. 14 mm is 0.551 inches, which is roughly half an inch. Exactly 1 inch is 25.4 mm — 14 mm is almost half that size.
1 inch is exactly 25.4 mm. This is a defined constant, in force since 1959 as the international inch, adopted by the US, the UK, Canada, Australia, and other English-speaking countries.
The formula is: inches = millimeters ÷ 25.4. For example, 50 mm ÷ 25.4 = 1.969 inches. The other way around: millimeters = inches × 25.4.
Not exactly. 1/2 inch is 12.7 mm, while 12 mm is 0.472 inches. The difference is 0.7 mm, which can matter when picking a drill bit or bolt.
No. 1/16 inch is 1.5875 mm, while 2 mm is 0.079 inches (almost 5/64 inch). The values are similar but not identical — the difference is about 0.41 mm.
No. 1 inch is exactly 25.4 mm, while 32 mm is 1.26 inches. That is more than 20% larger than 1 inch.
Quick approximation: divide the millimeters by 25 instead of 25.4. The error is minimal (about 1.6%), which is enough for a rough comparison. For example, 100 mm ÷ 25 = 4 inches (the exact value is 3.937). For precise conversions, always use the converter.
If you spot an error in the tables or have an idea for improving the converter, get in touch. We reply to every message.
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