Exact, not rounded
The inch is defined as exactly 2.54 cm (25.4 mm). So the conversions below are exact, not approximations:
| Inches | Centimetres |
|---|---|
| 1 | 2.54 |
| 4 | 10.16 |
| 12 (1 foot) | 30.48 |
| 36 (1 yard) | 91.44 |
The 4 inch and 10 cm question
Knitting and crochet patterns give gauge over 4 inches or 10 cm. They are close but not the same: 4 inches is 10.16 cm. Over a whole sweater the difference can add up, so the stitch-gauge calculator works out each one separately.
To go the other way, divide centimetres by 2.54: 10 cm ÷ 2.54 ≈ 3.94 inches. This displayed result is rounded; the conversion factor is exact.