Inches to cm converter and conversion chart
Last reviewed on 2026-08-28.
Need to convert inches to cm? 1 inch = 2.54 centimeters, exactly. Type a value in either box below to convert inches to centimeters or centimeters to inches, or scroll down for the conversion chart, the formula, and a guide to reading cm and inches on the same ruler.
Edit either field. Results are rounded to 4 decimal places.
The inch and the centimeter are both everyday units of length, but they belong to different systems. The inch is part of the US customary and imperial systems; the centimeter is part of the metric system (specifically the SI, as a sub-unit of the meter). Since 1959 the two have been tied together by an exact international agreement.
The exact definition
By the 1959 international yard-and-pound agreement, 1 inch is exactly 25.4 millimeters, which is exactly 2.54 centimeters. That's the definition every modern standards body, metrology lab, and scientific publication uses. Any conversion factor you see with more decimals than that is derived from this exact value.
Quick facts
1 inch = 2.54 cm (exact)
1 cm = 0.39370078740157… inch (repeating pattern because 1/2.54 is irrational in decimal)
1 foot (12 inches) = 30.48 cm (exact)
1 yard (36 inches) = 91.44 cm (exact)
Formulas
To convert inches to centimeters, multiply by 2.54:
cm = inches × 2.54
To convert centimeters to inches, divide by 2.54 (or multiply by the reciprocal, approximately 0.393701):
inches = cm ÷ 2.54
These formulas are exact; any precision you see is limited only by how many decimal places you keep in the result.
Inch to centimeter table
| Inches | Centimeters | Millimeters | Note |
|---|---|---|---|
| 1/16" | 0.15875 cm | 1.5875 mm | Finest tick on a typical imperial ruler |
| 1/8" | 0.3175 cm | 3.175 mm | |
| 1/4" | 0.635 cm | 6.35 mm | |
| 1/2" | 1.27 cm | 12.7 mm | |
| 3/4" | 1.905 cm | 19.05 mm | |
| 1" | 2.54 cm | 25.4 mm | |
| 2" | 5.08 cm | 50.8 mm | |
| 3" | 7.62 cm | 76.2 mm | |
| 4" | 10.16 cm | 101.6 mm | |
| 5" | 12.7 cm | 127 mm | |
| 6" | 15.24 cm | 152.4 mm | Standard school ruler |
| 8" | 20.32 cm | 203.2 mm | |
| 10" | 25.4 cm | 254 mm | |
| 11" | 27.94 cm | 279.4 mm | US Letter short edge height: 8.5" × 11" |
| 12" | 30.48 cm | 304.8 mm | 1 foot |
| 24" | 60.96 cm | 609.6 mm | 2 feet |
| 36" | 91.44 cm | 914.4 mm | 1 yard |
Centimeter to inch table
| Centimeters | Inches (decimal) | Inches (fractional, nearest 1/16) |
|---|---|---|
| 1 cm | 0.3937" | ≈ 6/16" (3/8") |
| 2 cm | 0.7874" | ≈ 13/16" |
| 2.54 cm | 1.0000" | 1" |
| 5 cm | 1.9685" | ≈ 1 15/16" |
| 10 cm | 3.9370" | ≈ 3 15/16" |
| 15 cm | 5.9055" | ≈ 5 15/16" |
| 20 cm | 7.8740" | ≈ 7 7/8" |
| 21 cm | 8.2677" | ≈ 8 1/4" |
| 25 cm | 9.8425" | ≈ 9 13/16" |
| 29.7 cm | 11.6929" | A4 long edge: 21 × 29.7 cm |
| 30 cm | 11.8110" | ≈ 11 13/16" |
| 50 cm | 19.685" | ≈ 19 11/16" |
| 100 cm (1 m) | 39.3701" | ≈ 39 3/8" |
How many cm are in an inch on a ruler?
Every inch on a ruler is 2.54 cm, so an inch mark never lines up exactly with a whole centimeter mark. On a ruler that prints both scales, the 1" mark sits just past the 2.5 cm line, the 2" mark just past 5 cm, the 4" mark just under 10.2 cm, and the 12" end of a standard foot ruler is at 30.48 cm — which is why a "30 cm ruler" and a "12 inch ruler" are almost, but not quite, the same length.
| Inch mark on the ruler | Where it falls on the cm scale |
|---|---|
| 1" | 2.54 cm — a little past 2.5 cm |
| 2" | 5.08 cm — just past 5 cm |
| 3" | 7.62 cm |
| 4" | 10.16 cm — about 1.6 mm past 10 cm |
| 6" | 15.24 cm — half a foot |
| 8" | 20.32 cm |
| 10" | 25.4 cm |
| 12" | 30.48 cm — end of a one-foot ruler |
Reading cm and inches on the same ruler
Inch scales are divided into halves, quarters, eighths, and sixteenths; centimeter scales are divided into ten millimeters. To read across scales, convert first and then find the mark: 24 cm ÷ 2.54 = 9.45 inches, which is between the 7/16" and 1/2" ticks after the 9" mark (9 7/16" is 9.4375"). Going the other way, 2.5 inches × 2.54 = 6.35 cm, i.e. the third and a half millimeter tick after 6 cm. The on-screen ruler does this for you: place the red line at a value and flip the IN/CM switch to read it in the other unit. For finding decimal inch values such as 3.54" between the fraction ticks, see how to read a ruler in inches.
A mental shortcut
For quick estimation without a calculator, most people can internalize these:
- 1 cm is a bit more than 3⁄8" — closer to 13⁄32".
- 1 inch is about 2.5 cm; think "an inch is a little more than two and a half centimeters."
- 4 inches ≈ 10 cm (off by only about 1.6 mm).
- A 12-inch ruler is a little longer than 30 cm (30.48 cm).
That 4 in ≈ 10 cm rule is handy: doubling gives you 8 in ≈ 20 cm, and tripling gives you 12 in ≈ 30 cm, each with small corrections.
Rounding and significant figures
In everyday contexts, rounding cm ↔ inch to one decimal place is almost always more than accurate enough. A physical ruler's finest practical reading is about 0.5 mm (0.02 inch); reporting more precision than that implies accuracy you don't actually have.
In technical contexts, follow the rounding convention of the field. Mechanical drawings often specify three decimals of an inch or two decimals of a millimeter; medical and scientific contexts usually specify whole millimeters or tenths.
Where inches and centimeters are used
Inches remain the default day-to-day length unit in the United States, and are still used alongside metric units in the United Kingdom and Canada for many consumer applications (screen sizes, clothing, construction lumber in imperial markets, tire sizes, plumbing fittings). Centimeters and millimeters are the default everywhere else and throughout scientific, medical, and technical work globally. Screen diagonals (13.3", 15.6", 55") and many hardware fasteners in imperial markets stay in inches regardless of local convention.
Related references
- Millimeters ↔ inches — for smaller measurements.
- Screen PPI, DPI, and device pixel ratio — why an on-screen ruler needs calibration.
- How accurate is an on-screen ruler? — realistic expectations.
- How to read a ruler in inches — decimal inches to the nearest 1/16.
- The ruler itself — open it, calibrate it, and start measuring.