Enter a value in inches or millimetres and the converter instantly shows the result both ways. The inch field also accepts fractions, e.g. 3/8 or 1 1/2.
1 inch (1″) = 25.4 mmEnter a value to see the conversion. Formula: mm = inches × 25.4, and inches = mm ÷ 25.4.
The conversion relies on a single constant: 1 inch equals exactly 25.4 millimetres. To convert inches to millimetres, multiply by 25.4; to convert millimetres to inches, divide by 25.4.
| Inch | Decimal | mm | Inch | Decimal | mm |
|---|---|---|---|---|---|
| 1/64″ | 0.0156 | 0.40 | 33/64″ | 0.5156 | 13.10 |
| 1/32″ | 0.0312 | 0.79 | 17/32″ | 0.5312 | 13.49 |
| 3/64″ | 0.0469 | 1.19 | 35/64″ | 0.5469 | 13.89 |
| 1/16″ | 0.0625 | 1.59 | 9/16″ | 0.5625 | 14.29 |
| 5/64″ | 0.0781 | 1.98 | 37/64″ | 0.5781 | 14.68 |
| 3/32″ | 0.0938 | 2.38 | 19/32″ | 0.5938 | 15.08 |
| 7/64″ | 0.1094 | 2.78 | 39/64″ | 0.6094 | 15.48 |
| 1/8″ | 0.1250 | 3.18 | 5/8″ | 0.6250 | 15.88 |
| 9/64″ | 0.1406 | 3.57 | 41/64″ | 0.6406 | 16.27 |
| 5/32″ | 0.1562 | 3.97 | 21/32″ | 0.6562 | 16.67 |
| 11/64″ | 0.1719 | 4.37 | 43/64″ | 0.6719 | 17.07 |
| 3/16″ | 0.1875 | 4.76 | 11/16″ | 0.6875 | 17.46 |
| 13/64″ | 0.2031 | 5.16 | 45/64″ | 0.7031 | 17.86 |
| 7/32″ | 0.2188 | 5.56 | 23/32″ | 0.7188 | 18.26 |
| 15/64″ | 0.2344 | 5.95 | 47/64″ | 0.7344 | 18.65 |
| 1/4″ | 0.2500 | 6.35 | 3/4″ | 0.7500 | 19.05 |
| 17/64″ | 0.2656 | 6.75 | 49/64″ | 0.7656 | 19.45 |
| 9/32″ | 0.2812 | 7.14 | 25/32″ | 0.7812 | 19.84 |
| 19/64″ | 0.2969 | 7.54 | 51/64″ | 0.7969 | 20.24 |
| 5/16″ | 0.3125 | 7.94 | 13/16″ | 0.8125 | 20.64 |
| 21/64″ | 0.3281 | 8.33 | 53/64″ | 0.8281 | 21.03 |
| 11/32″ | 0.3438 | 8.73 | 27/32″ | 0.8438 | 21.43 |
| 23/64″ | 0.3594 | 9.13 | 55/64″ | 0.8594 | 21.83 |
| 3/8″ | 0.3750 | 9.53 | 7/8″ | 0.8750 | 22.23 |
| 25/64″ | 0.3906 | 9.92 | 57/64″ | 0.8906 | 22.62 |
| 13/32″ | 0.4062 | 10.32 | 29/32″ | 0.9062 | 23.02 |
| 27/64″ | 0.4219 | 10.72 | 59/64″ | 0.9219 | 23.42 |
| 7/16″ | 0.4375 | 11.11 | 15/16″ | 0.9375 | 23.81 |
| 29/64″ | 0.4531 | 11.51 | 61/64″ | 0.9531 | 24.21 |
| 15/32″ | 0.4688 | 11.91 | 31/32″ | 0.9688 | 24.61 |
| 31/64″ | 0.4844 | 12.30 | 63/64″ | 0.9844 | 25.00 |
| 1/2″ | 0.5000 | 12.70 | 1″ | 1.0000 | 25.40 |
| Inches | mm | Inches | mm | Inches | mm |
|---|---|---|---|---|---|
| 1″ | 25.4 | 21″ | 533.4 | 41″ | 1041.4 |
| 2″ | 50.8 | 22″ | 558.8 | 42″ | 1066.8 |
| 3″ | 76.2 | 23″ | 584.2 | 43″ | 1092.2 |
| 4″ | 101.6 | 24″ | 609.6 | 44″ | 1117.6 |
| 5″ | 127.0 | 25″ | 635.0 | 45″ | 1143.0 |
| 6″ | 152.4 | 26″ | 660.4 | 46″ | 1168.4 |
| 7″ | 177.8 | 27″ | 685.8 | 47″ | 1193.8 |
| 8″ | 203.2 | 28″ | 711.2 | 48″ | 1219.2 |
| 9″ | 228.6 | 29″ | 736.6 | 49″ | 1244.6 |
| 10″ | 254.0 | 30″ | 762.0 | 50″ | 1270.0 |
| 11″ | 279.4 | 31″ | 787.4 | 51″ | 1295.4 |
| 12″ | 304.8 | 32″ | 812.8 | 52″ | 1320.8 |
| 13″ | 330.2 | 33″ | 838.2 | 53″ | 1346.2 |
| 14″ | 355.6 | 34″ | 863.6 | 54″ | 1371.6 |
| 15″ | 381.0 | 35″ | 889.0 | 55″ | 1397.0 |
| 16″ | 406.4 | 36″ | 914.4 | 56″ | 1422.4 |
| 17″ | 431.8 | 37″ | 939.8 | 57″ | 1447.8 |
| 18″ | 457.2 | 38″ | 965.2 | 58″ | 1473.2 |
| 19″ | 482.6 | 39″ | 990.6 | 59″ | 1498.6 |
| 20″ | 508.0 | 40″ | 1016.0 | 60″ | 1524.0 |
Conversion the other way – how many inches a given millimetre dimension is (rounded to 3 decimals).
| mm | Inches | mm | Inches |
|---|---|---|---|
| 8 mm | 0.315″ | 10 mm | 0.394″ |
| 12 mm | 0.472″ | 16 mm | 0.63″ |
| 20 mm | 0.787″ | 22 mm | 0.866″ |
| 24 mm | 0.945″ | 25 mm | 0.984″ |
| 26 mm | 1.024″ | 27 mm | 1.063″ |
| 28 mm | 1.102″ | 30 mm | 1.181″ |
| 32 mm | 1.26″ | 35 mm | 1.378″ |
| 38 mm | 1.496″ | 40 mm | 1.575″ |
| 43 mm | 1.693″ | 46 mm | 1.811″ |
| 50 mm | 1.969″ | 51 mm | 2.008″ |
| 52 mm | 2.047″ | 57 mm | 2.244″ |
| 58 mm | 2.283″ | 60 mm | 2.362″ |
| 63 mm | 2.48″ | 65 mm | 2.559″ |
| 76 mm | 2.992″ | 90 mm | 3.543″ |
One inch (1″) is exactly 25.4 mm — a fixed value defined in 1959.
Multiply the number of inches by 25.4. Formula: mm = inches × 25.4. Example: 3 × 25.4 = 76.2 mm.
Divide the number of millimetres by 25.4. Formula: inches = mm ÷ 25.4. Example: 50 ÷ 25.4 ≈ 1.97″.
3/8 inch is 9.53 mm (0.375″ × 25.4).
1/2 inch is 12.7 mm (0.5″ × 25.4).
3/4 inch is 19.05 mm (0.75″ × 25.4).
1/4 inch is 6.35 mm (0.25″ × 25.4).
1/8 inch is 3.18 mm (0.125″ × 25.4).
5/8 inch is 15.88 mm (0.625″ × 25.4).
1 1/2 inches (1.5″) is 38.1 mm. The same applies to the 6/4″ notation.
1 1/4 inches (1.25″, i.e. 5/4″) is 31.75 mm.
No. In pipe-thread designations (e.g. G 1/2″, BSP) the inch is a nominal size, not the actual outside diameter. The 25.4 mm conversion applies to length.
