Convert between metric and imperial length units: millimeters, centimeters, meters, inches, feet, miles, and more.
Last updated: March 2026 | By Patchworkr Team
Length measurement uses two main systems: metric (meters) and imperial (feet/inches). The metric system is based on powers of 10, making conversions simple. Imperial units have historical origins with less systematic relationships.
The meter is the SI base unit of length, defined as the distance light travels in vacuum in 1/299,792,458 of a second. All other metric units are decimal multiples: 1 km = 1000 m, 1 cm = 0.01 m, etc.
Imperial units include inches, feet, yards, and miles, with complex conversion factors: 12 inches = 1 foot, 3 feet = 1 yard, 1760 yards = 1 mile. The international inch is defined as exactly 2.54 centimeters.
1 meter = 3.28084 feet. This is exact based on the definition that 1 inch = 2.54 cm. For quick estimates, remember 1 m ≈ 3.3 ft.
The 12-inch foot comes from ancient measurement systems. Twelve is highly divisible (by 2, 3, 4, 6), making it practical for construction and commerce before decimal systems.
No, both systems can be equally accurate. The metric system is more convenient because it uses base-10, making mental math and conversions easier. Most scientific work uses metric.
A nautical mile (1.852 km) is based on one minute of latitude. It's used in aviation and maritime navigation because it relates directly to the Earth's coordinate system.
A nanometer (nm) is 1 billionth of a meter (10⁻⁹ m). It's used to measure wavelengths of light, atomic structures, and semiconductor features. A DNA helix is about 2 nm wide.
Only the United States, Liberia, and Myanmar officially use imperial units. The UK uses a mix (miles for roads, metric for most else). Almost all other countries use metric exclusively.
Related Tools
Convert between decimeters and meters.
Calculate and convert feet and inches.
Convert between feet and inches.
Convert between inches and centimeters.
Convert light-years to parsecs, AU, kilometers, and other cosmic distances.
Convert between centimeters and inches.