Inches to Millimeters (in to mm)
1 in = 25.4 mm
and 1 mm = 0.0393701 in
How to convert Inches to Millimeters
mm = in × 25.4
To convert, multiply the number of inches by 25.4. Example: 10 in × 25.4 = 254 mm.
1 inch is exactly 25.4 millimeters by definition.
Essential in workshops: fractional-inch drill bits, sockets, pipe and lumber sizes are matched to metric parts this way.
Mental shortcut: multiply by 25 (underestimates by about 1.6%).
Inches to Millimeters conversion chart
| Inches | Millimeters |
|---|---|
| 1/16 in | 1.59 mm |
| 1/8 in | 3.18 mm |
| 3/16 in | 4.76 mm |
| 1/4 in | 6.35 mm |
| 5/16 in | 7.94 mm |
| 3/8 in | 9.52 mm |
| 7/16 in | 11.11 mm |
| 1/2 in | 12.7 mm |
| 9/16 in | 14.29 mm |
| 5/8 in | 15.88 mm |
| 11/16 in | 17.46 mm |
| 3/4 in | 19.05 mm |
| 13/16 in | 20.64 mm |
| 7/8 in | 22.22 mm |
| 15/16 in | 23.81 mm |
| 1 in | 25.4 mm |
| 1 1/4 in | 31.75 mm |
| 1 1/2 in | 38.1 mm |
| 1 3/4 in | 44.45 mm |
| 2 in | 50.8 mm |
| 2 1/4 in | 57.15 mm |
| 2 1/2 in | 63.5 mm |
| 2 3/4 in | 69.85 mm |
| 3 in | 76.2 mm |
| 3 1/4 in | 82.55 mm |
| 3 1/2 in | 88.9 mm |
| 3 3/4 in | 95.25 mm |
| Inches | Millimeters |
|---|---|
| 4 in | 101.6 mm |
| 4 1/4 in | 107.95 mm |
| 4 1/2 in | 114.3 mm |
| 4 3/4 in | 120.65 mm |
| 5 in | 127 mm |
| 5 1/4 in | 133.35 mm |
| 5 1/2 in | 139.7 mm |
| 5 3/4 in | 146.05 mm |
| 6 in | 152.4 mm |
| 7 in | 177.8 mm |
| 8 in | 203.2 mm |
| 9 in | 228.6 mm |
| 10 in | 254 mm |
| 11 in | 279.4 mm |
| 12 in | 304.8 mm |
| 13 in | 330.2 mm |
| 14 in | 355.6 mm |
| 15 in | 381 mm |
| 16 in | 406.4 mm |
| 17 in | 431.8 mm |
| 18 in | 457.2 mm |
| 19 in | 482.6 mm |
| 20 in | 508 mm |
| 21 in | 533.4 mm |
| 22 in | 558.8 mm |
| 23 in | 584.2 mm |
| 24 in | 609.6 mm |
Values rounded to 2 decimal places (4 below 1). Use the converter above for more precision.
Frequently asked questions
How many millimeters are in 1 inch?
1 inch = 25.4 millimeters. 1 inch is exactly 25.4 millimeters by definition.
How do I convert inches to millimeters?
Multiply the number of inches by 25.4. Example: 10 in × 25.4 = 254 mm.
Is there a quick way to estimate in to mm in your head?
Yes — multiply by 25. This underestimates by about 1.6%. Use the exact formula (mm = in × 25.4) when precision matters.
How do I convert millimeters back to inches?
Use in = mm ÷ 25.4 — divide the number of millimeters by 25.4. See the Millimeters to Inches page for a full chart.