Inch (in)

Definition

Exactly 2.54 centimeters (0.0254 m), by the 1959 international agreement.

History

The inch takes its name from the Latin uncia, a twelfth part, and has always been one twelfth of a foot. The 1959 agreement fixed it at exactly 2.54 centimeters.

Where it is used

Inches are used for screen and TV sizes worldwide, and in the United States for height, lumber and hardware.

Typical uses include screen sizes, height, lumber and hardware.

Conversion pages

These pages convert inch to or from another unit in length.

• Centimeter to inch
• Millimeter to inch
• Inch to foot

Other Length units

• Meter (m)
• Centimeter (cm)
• Millimeter (mm)
• Kilometer (km)
• Foot (ft)
• Yard (yd)
• Mile (mi)

Sources

• NIST HB 44 International Yard and Pound Agreement (1959); NIST Handbook 44, App. C · Dataset reviewed Nov 11, 2026