The official rule is 1 inch = 2.54 cm. For quick estimates, remember ×2.5.
How to do it fast
4 in → 4 × 2.5 = 10 cm (exact is 10.16 cm)
10 in → 10 × 2.5 = 25 cm (exact is 25.4 cm)
Handy memory chart
1 in = 2.54 cm
6 in ≈ 15 cm
12 in (1 ft) ≈ 30 cm
40 in ≈ 1 m (actually 101.6 cm)
When you need exact
Use our Length Converter for precise results and more units (mm, m, ft): /length-converter
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