Published September 5, 2026
12 inches in cm - and other everyday conversions
12 inches is exactly 30.48 cm. This is the length of a standard 1-foot ruler, and it is the conversion people search for more than any other ruler size. The math: 1 inch is defined as exactly 2.54 cm, so 12 x 2.54 = 30.48.
Quick reference: inches to cm
| Inches | cm |
|---|---|
| 1 in | 2.54 cm |
| 2 in | 5.08 cm |
| 3 in | 7.62 cm |
| 4 in | 10.16 cm |
| 5 in | 12.70 cm |
| 6 in | 15.24 cm |
| 8 in | 20.32 cm |
| 10 in | 25.40 cm |
| 12 in | 30.48 cm |
| 24 in | 60.96 cm |
Why 2.54?
The inch is defined by international agreement as exactly 2.54 centimeters. That makes every conversion between inches and cm exact - no rounding until you choose a precision. For example, 12 inches is not “about” 30.48 cm; it is 30.48 cm.
Everyday uses
- A 12-inch ruler (30.48 cm) is the standard classroom and workshop ruler.
- A 6-inch ruler (15.24 cm) is the size of most phone screens measured diagonally in inches.
- A 30 cm ruler is 11.81 inches - shorter than a foot by just 0.48 cm.
- A credit card is 3.37 inches (8.56 cm) wide - useful for rough measurements anywhere.
Don’t do the math - use both scales at once
The fastest way to convert while measuring is to read both scales on the same ruler. The online ruler draws a centimeter/millimeter scale and an inch scale together, calibrated to your screen - so 12 inches and 30.48 cm appear on the same object, automatically. For a printable version, see the printable ruler.
Ready to measure? Open the online ruler, calibrate it once against a credit card, and start measuring in cm, mm, or inches.