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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9 mm = 0.3543 in
Worked example
9 ÷ 25.4 = 0.3543 inches. On a ruler marked in sixteenths, that is about 3/8″; in thirty-seconds, 11/32″; in sixty-fourths, 23/64″. The nearest 1/16 mark (3/8″ = 9.52 mm) is off by 0.52 mm.
9 mm is also 0.9 cm.
| Millimeters | Inches | Nearest 1/16 |
|---|---|---|
| 4 mm | 0.1575 | 3/16″ |
| 5 mm | 0.1969 | 3/16″ |
| 6 mm | 0.2362 | 1/4″ |
| 7 mm | 0.2756 | 1/4″ |
| 8 mm | 0.315 | 5/16″ |
| 9 mm | 0.3543 | 3/8″ |
| 10 mm | 0.3937 | 3/8″ |
| 11 mm | 0.4331 | 7/16″ |
| 12 mm | 0.4724 | 1/2″ |
| 13 mm | 0.5118 | 1/2″ |
| 14 mm | 0.5512 | 9/16″ |
Frequently asked questions
How many inches is 9 mm?
0.3543 inches, about 3/8″.
What fraction of an inch is 9 mm?
About 11/32″ to the nearest 1/32.