Where do these numbers come from?
- NISTSP 811 exact unit definitions (1 in = 25.4 mm, 1 lb = 453.59237 g)current edition
- NISTHandbook 44, weights and measurescurrent edition
- King Arthur BakingIngredient Weight Chart (kitchen tools)retrieved Oct 23, 2026
Checked Oct 23, 2026. 1 inch is exactly 25.4 mm (NIST SP 811), so 100 mm ÷ 25.4 = 3.937 in.
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1 mm = 0.0394 in
Worked example
1 ÷ 25.4 = 0.0394 inches. On a ruler marked in sixteenths, that is about 1/16″; in thirty-seconds, 1/32″; in sixty-fourths, 3/64″. The nearest 1/16 mark (1/16″ = 1.59 mm) is off by 0.59 mm.
1 mm is also 0.1 cm.
| Millimeters | Inches | Nearest 1/16 |
|---|---|---|
| 1 mm | 0.0394 | 1/16″ |
| 2 mm | 0.0787 | 1/16″ |
| 3 mm | 0.1181 | 1/8″ |
| 4 mm | 0.1575 | 3/16″ |
| 5 mm | 0.1969 | 3/16″ |
| 6 mm | 0.2362 | 1/4″ |
Frequently asked questions
How many inches is 1 mm?
0.0394 inches, about 1/16″.
What fraction of an inch is 1 mm?
About 1/32″ to the nearest 1/32.