Inches to Millimeters
Type inches (in), see millimeters (mm).
By Akash Yadav Updated 27 September 2026
Type a number above to see the answer.
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The formula
How to convert inches to millimeters
To change inches into millimeters, multiply by 25.4.
millimeters = inches × 25.4
Going the other way: inches = millimeters ÷ 25.4
1 inch = 25.4 millimeters. This factor is the exact definition of the unit, not a rounded estimate.
Worked example
You have 0.75 inches. Multiply by 25.4. 0.75 × 25.4 = 19.05 mm.
Common values
Inches to millimeters conversion table
| Inches (in) | Millimeters (mm) |
|---|---|
| 0.0625 in | 1.5875 mm |
| 0.125 in | 3.175 mm |
| 0.1875 in | 4.7625 mm |
| 0.25 in | 6.35 mm |
| 0.375 in | 9.525 mm |
| 0.5 in | 12.7 mm |
| 0.625 in | 15.875 mm |
| 0.75 in | 19.05 mm |
| 1 in | 25.4 mm |
| 1.5 in | 38.1 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 6 in | 152.4 mm |
| 12 in | 304.8 mm |
Before you rely on it
Fractions of an inch: type them as decimals
1 inch is exactly 25.4 mm by the international agreement of 1959, so every answer on this page is exact — nothing is rounded except the decimals you choose to show.
Rulers and drill sets mark fractions. Divide the top number by the bottom one before typing: 3/8 in is 0.375, which is 9.525 mm. The table above covers the common ones from 1/16 inch up.
For a measurement like 2 3/4 in, add the whole inches to the fraction first: 2 + 0.75 = 2.75 in, which is 69.85 mm.
Screens and wheels are sized in inches even in metric countries. A 27-inch monitor measures 685.8 mm corner to corner; the width is less, because the size is always the diagonal.
Common questions
Frequently asked questions
How many mm is 1 inch?
1 inch is exactly 25.4 mm.
How many mm is 1/4 inch?
1/4 inch is exactly 6.35 mm.
How many mm is 1/2 inch?
1/2 inch is exactly 12.7 mm.
How many mm is 3/8 inch?
3/8 inch is exactly 9.525 mm.
How many mm is 1/8 inch?
1/8 inch is exactly 3.175 mm.
How many mm is 3/4 inch?
3/4 inch is exactly 19.05 mm.
Keep going
Related converters
- Millimeters to Inches mm → in
- Inches to Centimeters in → cm
- Centimeters to Inches cm → in
- All length converters
Every factor on this page is listed in our conversion methodology.