What this does
Type a length in centimeters and see it in inches immediately. The math is exact: 1 inch = 2.54 cm by definition, so inches = cm ÷ 2.54, which is the same as cm × 0.393701. The page opens with 1 cm entered and 0.393701 in the inches box. Edit either side and the other recomputes on every keystroke; ⇄ swaps the units and keeps the number on the left. Results are rounded to six decimal places. It runs entirely in your browser and works offline.
How do I convert cm to inches by hand?
Divide by 2.54. For a quick estimate, multiply by 4 and drop the last digit: 45 cm → 180 → 18 in (real 17.7). That's about two percent high, so shave a little off. Another anchor: 10 cm is 3.94 in, near enough to "4 inches" that you can count in tens — 30 cm is a hair under 12 in, which is why a school ruler is 30 cm on one edge and 12 in on the other.
Centimeters to inches at a glance
| Centimeters | Inches | Context |
|---|---|---|
| 5 | 1.968504 | a 5 cm hem allowance |
| 20 | 7.874016 | the depth of most carry-on limits |
| 35 | 13.779528 | a laptop sleeve, a small pizza |
| 56 | 22.047244 | IATA carry-on length |
| 100 | 39.370079 | one meter |
| 160 | 62.992126 | 5 ft 3 in |
| 175 | 68.897638 | 5 ft 9 in |
| 190 | 74.80315 | 6 ft 3 in |
How tall is 170 cm in feet and inches?
5 ft 7 in. Here's the working with the tool's actual output: 170 ÷ 2.54 = 66.929133858…, displayed as 66.929134 in. Divide by 12 for the feet — 5, with 6.929134 in left over — so 170 cm is 5 ft 6.9 in, which rounds to 5′7″. Same steps for other heights: 165 cm = 64.96063 in = 5 ft 5 in; 180 cm = 70.866142 in = 5′11″; 185 cm = 72.834646 in = 6′1″. Round to the nearest inch for forms.
Is a 55 × 40 × 20 cm carry-on within US airline limits?
Probably not. 55 × 40 × 20 cm converts to 21.65 × 15.75 × 7.87 in, and the common US carry-on limit is 22 × 14 × 9 in. The length fits and the depth has an inch spare, but the width is almost two inches over. Check the specific airline before you fly — some measure the total of the three dimensions rather than each one, and 45.3 in total is usually fine.
Why is an inch exactly 2.54 cm?
Until 1959 the US and UK inches differed by about two millionths, enough to matter in precision engineering. The International Yard and Pound Agreement fixed the yard at 0.9144 m, making the inch exactly 25.4 mm in every English-speaking country at once. Since then the conversion has been pure arithmetic with no measurement error — the only rounding is the tool's six-decimal display, which only matters when 2.54 doesn't divide the number cleanly.
Where does cm to inches come up in real life?
Reading heights on European CVs, dating profiles and ID documents; clothing charts from EU and Asian retailers, which give chest, waist and inseam in centimeters; furniture from IKEA; baby length on a metric growth chart; and luggage rules from a non-US airline. The opposite direction — product screen sizes and hardware in inches — is on the inches to cm page. This page hides the category tabs but keeps every length unit in the dropdowns; for weight, temperature and the rest use the full unit converter.