cm to inches converter

cm to inches in one step: 1 cm is 0.3937 inch, because 1 inch is exactly 2.54 cm. Enter centimeters and see inches while you type, with the nearest sixteenth of an inch for a tape measure – 100 cm = 39.37 in. Inches to cm works in the same box.

Example: Length 100 · Direction: cm to inches (cm → in) → Answer: 100 cm = 39.37 in. Source: NIST SP 811, Appendix B.8 – inch = 2.54 cm (exact, international agreement of 1959). Updated: 5 October 2026.

Length

Direction

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Result

Answer: 100 cm = 39.37 in
On a tape measure: Nearest 1/16 inch: 39 3/8 in, which is 0.01 cm away from the exact length.
Working: 100 cm ÷ 2.54 = 39.37 in
Quick check in your head: 100 × 0.4 ≈ 40 in (exact: 39.37 in). Multiplying by 0.4 comes out about 1.6 % high.
Conversion chart: cm in
1 0.3937
2 0.7874
2.5 0.9843
5 1.969
10 3.937
15 5.906
20 7.874
25 9.843
30 11.811
40 15.748
50 19.685
60 23.622
75 29.528
100 39.37
150 59.055
170 66.929
180 70.866
200 78.74
Everyday sizes in cm and inches: Size cm in
Bank card width (ISO/IEC 7810, 85.6 mm) 8.56 3.37
A4 paper, width 21 8.268
A4 paper, height 29.7 11.693
A 30 cm school ruler 30 11.811
Typical cabin bag limit, longest side 55 21.654
Waist of 80 cm (trouser size) 80 31.496
Body height of 170 cm 170 66.929; One inch is defined as exactly 2.54 cm (international agreement of 1959), so inches to cm is exact; cm to inches is rounded for display.

cm	in
1	0.3937
2	0.7874
2.5	0.9843
5	1.969
10	3.937
15	5.906
20	7.874
25	9.843
30	11.811
40	15.748
50	19.685
60	23.622
75	29.528
100	39.37
150	59.055
170	66.929
180	70.866
200	78.74

Size	cm	in
Bank card width (ISO/IEC 7810, 85.6 mm)	8.56	3.37
A4 paper, width	21	8.268
A4 paper, height	29.7	11.693
A 30 cm school ruler	30	11.811
Typical cabin bag limit, longest side	55	21.654
Waist of 80 cm (trouser size)	80	31.496
Body height of 170 cm	170	66.929

How it is calculated

How to convert cm to inches

inches = centimeters ÷ 2.54, or centimeters × 0.3937. For 100 cm: 100 ÷ 2.54 = 39.37 in. Going back, centimeters = inches × 2.54: 12 in × 2.54 = 30.48 cm. The 2.54 is exact: one inch has been defined as 25.4 mm since 1959.

Metric sizes you meet in US shops

Paper, cards and luggage come in metric sizes, and shop listings want inches. A4 paper is 21 × 29.7 cm, which is 8.268 × 11.693 in – a little narrower and taller than US Letter (8.5 × 11 in). A bank card is 8.56 cm wide, 3.37 in. A cabin bag of 55 cm is 21.654 in, and an 80 cm waist is 31.496 in, so size 31 or 32 in US trousers.

Reading the result on a tape measure

A tape does not show 21.654 in, it shows 21 5/8 in. The line “On a tape measure” rounds to the nearest sixteenth of an inch and tells you the error in cm. For 55 cm (21.654 in) the nearest 1/16 is 21 5/8 in (21.625), 0.07 cm off – fine for woodwork, too coarse for engineering.

A quick mental trick

Multiply centimeters by 0.4: 50 cm × 0.4 = 20 in against 19.685 in exact. Going the other way multiply inches by 2.5: 10 in is about 25 cm (exact 25.4 cm). Both shortcuts are about 1.6 % off.

For body height in feet and inches use cm to feet. For millimeters see mm to inches; for screen sizes and fractions see inches to cm.

Frequently asked questions

How many inches is 1 cm?

1 cm is 0.3937 inch. 10 cm is 3.937 in, 50 cm is 19.685 in and 100 cm is 39.37 in.

How do I convert cm to inches?

Divide the centimeters by 2.54. Example: 30 cm ÷ 2.54 = 11.811 in.

How many inches is 170 cm?

170 cm is 66.929 in. As a body height that is 5 ft 6.9 in, see the cm to feet page.

How many inches is an A4 sheet?

A4 is 21 cm × 29.7 cm, which is 8.268 in × 11.693 in. US Letter paper is 8.5 in × 11 in, so A4 is narrower and longer.

How many cm is 1 inch?

Exactly 2.54 cm. Half an inch is 1.27 cm and 12 inches is 30.48 cm.

Sources and legal basis

As of: 5 October 2026 · Editorial policy