justyourconvertInches to MM
Inch sizes in millimeters, exact to the thousandth.
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Inches to mm
Convert inches to millimeters: multiply by 25.4
1 inch = 25.4 millimeters
Formula: mm = in × 25.4
Inches to millimeters table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 5 | 127 |
| 6 | 152.4 |
| 7 | 177.8 |
| 8 | 203.2 |
| 9 | 228.6 |
| 10 | 254 |
| 15 | 381 |
| 20 | 508 |
| 25 | 635 |
| 50 | 1,270 |
| 100 | 2,540 |
Calculated on your device with exact factors from NIST and the SI.
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How to convert Inches to mm
Three steps, all in your browser.
- 1
Type a number
Enter a value in either box; the other updates instantly.
- 2
Pick the units
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- 3
Copy the result
Copy the answer or read it off the conversion table.
Inches to MM: what to know
Many tools, pipes, drill bits and parts are sized in fractions of an inch, while metric drawings and calipers read in millimeters. To convert inches to millimeters, multiply by 25.4. The factor is exact: the international inch is defined as 25.4 mm (1959 agreement, adopted by NIST), so 1 inch is 25.4 mm with no rounding at all.
Common fractional sizes convert cleanly. 1/16 inch is 1.5875 mm, 1/8 inch is 3.175 mm, 1/4 inch is 6.35 mm, 3/8 inch is 9.525 mm, 1/2 inch is 12.7 mm and 3/4 inch is 19.05 mm. For a mixed number such as 2 5/8 inches, convert the fraction to a decimal (0.625), add the whole inches (2.625) and multiply: 2.625 × 25.4 = 66.675 mm.
Thousandths of an inch (thou or mils) are used in machining and for film and coating thickness. One thou is 0.0254 mm, so a tolerance of ±0.005 inch is ±0.127 mm. Pipe sizes are an exception: a 1/2-inch nominal pipe does not measure 12.7 mm, because nominal pipe sizes are trade names rather than measured diameters.
Popular uses
- Converting drill bit and socket sizes for a metric project
- Reading inch-based plans with a metric caliper
- Converting coating and film thickness from mils
- Specifying replacement parts from inch dimensions
Tips for the best result
- Turn fractions into decimals before converting: 7/16 = 0.4375.
- Nominal pipe and lumber sizes are names, not measurements; check the actual size.
- Results to 0.01 mm are enough for most workshop jobs.
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