Inch Converter

About Inches

The inch (in) is a unit of length in the imperial and United States customary systems of measurement. It is defined as exactly 25.4 millimeters. The inch is commonly used in the United States, Canada, and the United Kingdom for many everyday measurements.

The inch has a long history, with variations of its definition used by many cultures. The word “inch” came from the Latin word “uncia,” meaning “one-twelfth,” as the Roman inch was one-twelfth of a Roman foot. In 1959, the international yard and pound agreement defined the inch as exactly 25.4 millimeters, standardizing it across all English-speaking countries.

Inches are commonly used for:

• Construction and carpentry
• Screen sizes for televisions and monitors (measured diagonally)
• Paper sizes in the US (letter size is 8.5 × 11 inches)
• Height measurements in the US and partially in the UK
• Plumbing pipe diameters
• Rainfall measurements in the US

Traditionally, the inch was subdivided into smaller fractions:

• 1/2 inch (half inch)
• 1/4 inch (quarter inch)
• 1/8 inch (eighth inch)
• 1/16 inch (sixteenth inch)
• 1/32 inch (thirty-second inch)
• 1/64 inch (sixty-fourth inch)

In technical applications, inches are also divided decimally into tenths, hundredths, and thousandths of an inch.

To help visualize an inch:

• The width of a U.S. quarter is slightly less than 1 inch (about 0.955 inches)
• A standard paper clip is about 1 inch in length when not bent
• The top segment of an adult’s thumb is approximately 1 inch long
• A standard golf ball is about 1.68 inches in diameter