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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42 mm = 1.6535 in
Worked example
42 ÷ 25.4 = 1.6535 inches. On a ruler marked in sixteenths, that is about 1 5/8″; in thirty-seconds, 1 21/32″; in sixty-fourths, 1 21/32″. The nearest 1/16 mark (1 5/8″ = 41.27 mm) is off by 0.73 mm.
42 mm is also 4.2 cm.
| Millimeters | Inches | Nearest 1/16 |
|---|---|---|
| 37 mm | 1.4567 | 1 7/16″ |
| 38 mm | 1.4961 | 1 1/2″ |
| 39 mm | 1.5354 | 1 9/16″ |
| 40 mm | 1.5748 | 1 9/16″ |
| 41 mm | 1.6142 | 1 5/8″ |
| 42 mm | 1.6535 | 1 5/8″ |
| 43 mm | 1.6929 | 1 11/16″ |
| 44 mm | 1.7323 | 1 3/4″ |
| 45 mm | 1.7717 | 1 3/4″ |
| 46 mm | 1.811 | 1 13/16″ |
| 47 mm | 1.8504 | 1 7/8″ |
Frequently asked questions
How many inches is 42 mm?
1.6535 inches, about 1 5/8″.
What fraction of an inch is 42 mm?
About 1 21/32″ to the nearest 1/32.