How to Convert Inches to Centimeters

Since the international yard and pound agreement of 1959, one inch is exactly 2.54 centimeters, or 25.4 millimeters. There is no rounding in this number: it is the definition of the inch.

A foot is 12 inches, so one foot is exactly 30.48 cm. A yard is 3 feet, exactly 91.44 cm.

• Inches to centimeters: multiply by 2.54.
• Inches to millimeters: multiply by 25.4.
• Feet to centimeters: multiply by 30.48, or first change feet to inches (× 12) and then multiply by 2.54.
• Example: 10 in × 2.54 = 25.4 cm.
• Example: 3 ft = 36 in, and 36 × 2.54 = 91.44 cm.

For a length given in feet and inches, such as 2 ft 7 in, convert the feet to inches first, add the extra inches, and then multiply the total by 2.54. Converting the two parts separately and adding the results gives the same answer, but it is easier to make a mistake.

Divide centimeters by 2.54 to get inches. One centimeter is about 0.393701 in. For example, 50 cm ÷ 2.54 = 19.685 in.

To express the result in feet and inches, divide the total inches by 12. The whole number is the feet, and the remainder is the inches. For 100 cm: 39.3701 in is 3 ft and about 3.37 in.

Screen sizes are usually given as the diagonal in inches. A ruler marked 12 inches is one foot long. US letter paper is 8.5 by 11 inches.

US tape measures, drill bits and wrenches often use binary fractions of an inch. Write the fraction as a decimal and multiply by 25.4 to get millimeters.

• Dividing by 2.54 when you should multiply. A length in centimeters is always a larger number than the same length in inches.
• Reading 5.5 ft as 5 ft 5 in. A decimal foot is not inches: 5.5 ft is 5 ft 6 in, which is 167.64 cm.
• Mixing up centimeters and millimeters. Multiply inches by 2.54 for centimeters and by 25.4 for millimeters.
• Rounding 2.54 to 2.5. That makes every result about 1.6% too small.