Inch measurements come at you in awkward forms: fractions off a tape measure, screen sizes in product listings, paper and photo dimensions, or US-made parts with no metric equivalent printed on them. Converting to centimeters is always one multiplication by 2.54 — the trick is getting fractions into decimal form first and knowing what the number actually measures.
How to use the inches to cm converter
- Enter the measurement in Inches (in). For fractions, type the decimal: 1/4 = 0.25, 3/8 = 0.375, 5/8 = 0.625, 3/4 = 0.75.
- Read the answer in centimeters, plus millimeters and the same length in feet and inches.
- Below the result you will find a chart from 1/8 inch to 6 feet and a table of common screen diagonals in centimeters.
The inches to centimeters formula
Because the inch is defined as exactly 2.54 cm, the result carries no conversion error at all. Any rounding you see comes from the decimals displayed. Multiply by 25.4 instead if you want millimeters.
Worked example: a fractional tape-measure reading
A shelf bracket measures 5 3/8 inches.
Step 1. Convert the fraction: 3 ÷ 8 = 0.375, so the length is 5.375 in.
Step 2. Multiply: 5.375 × 2.54 = 13.6525 cm (136.525 mm).
Fractions of an inch in centimeters
US tape measures and rulers divide the inch into halves, quarters, eighths and sixteenths. These are the exact metric values:
| Fraction | Decimal inch | Centimeters |
|---|---|---|
| 1/16 | 0.0625 | 0.15875 |
| 1/8 | 0.125 | 0.3175 |
| 3/16 | 0.1875 | 0.47625 |
| 1/4 | 0.25 | 0.635 |
| 5/16 | 0.3125 | 0.79375 |
| 3/8 | 0.375 | 0.9525 |
| 1/2 | 0.5 | 1.27 |
| 5/8 | 0.625 | 1.5875 |
| 3/4 | 0.75 | 1.905 |
| 7/8 | 0.875 | 2.2225 |
Add these to the whole-inch value: 2 3/4 in is 2 × 2.54 + 1.905 = 6.985 cm.
Screen sizes are diagonals
TVs, monitors, laptops and phones are sold by the length of the screen’s diagonal in inches. A 55-inch TV has a diagonal of 55 × 2.54 = 139.7 cm, but it is narrower than that. For a 16:9 screen, the width is about 87% of the diagonal and the height about 49%, so a 65-inch set is roughly 143.9 cm wide and 80.9 cm tall. Measure the cabinet or wall space against the width, not the advertised size, and remember the bezel and stand add a little more. The screen size calculator works out width and height for any diagonal and aspect ratio.
US paper and photo sizes
| Size | Inches | Centimeters |
|---|---|---|
| Letter | 8.5 × 11 | 21.59 × 27.94 |
| Legal | 8.5 × 14 | 21.59 × 35.56 |
| Tabloid / ledger | 11 × 17 | 27.94 × 43.18 |
| 4 × 6 photo | 4 × 6 | 10.16 × 15.24 |
| 5 × 7 photo | 5 × 7 | 12.7 × 17.78 |
| 8 × 10 photo | 8 × 10 | 20.32 × 25.4 |
When a document designed for Letter is printed on A4, the page is 6 mm narrower and 18 mm taller, which is why margins sometimes shift or text gets scaled.
Estimating without a calculator
Multiply by 2.5 and then add a little: 2.5 is only 1.6% below 2.54. Twelve inches × 2.5 = 30, and the exact 30.48 is just half a centimeter more. For the reverse direction, use the cm to inches converter.
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54. The value is a definition, not a measurement, so 1 inch = 2.54 cm with no rounding. One inch is also exactly 25.4 millimeters.
How do I convert a fraction of an inch to cm?
Turn the fraction into a decimal first by dividing the top number by the bottom number, add any whole inches, then multiply by 2.54. For 5 3/8 in: 3 ÷ 8 = 0.375, so 5.375 × 2.54 = 13.6525 cm.
Does a 65-inch TV measure 65 inches wide?
No. Screen sizes are measured diagonally, corner to corner. A 65-inch 16:9 screen is 165.1 cm on the diagonal but only about 56.7 inches (143.9 cm) wide and 31.9 inches (80.9 cm) tall.
How many cm is 12 inches?
12 inches, which is one foot, equals exactly 30.48 cm.
What size is US Letter paper in centimeters?
US Letter is 8.5 × 11 inches, which is 21.59 × 27.94 cm. It is slightly wider and shorter than A4 (21.0 × 29.7 cm), the standard sheet in most other countries.