LengthConverter
Instantly convert length units including Millimeter, Centimeter, and more.
About Length Units
Length is one of the seven fundamental SI base quantities, measuring the extent of an object or the distance between two points in one dimension. The metric system defines the meter (m) as its base unit — today fixed by the speed of light — and builds all other length units from it by powers of ten. The imperial system, still used daily in the United States and partially in the United Kingdom, relies on inches, feet, yards, and miles, all rooted in ancient body-based standards that were formalized over centuries.
The story of length measurement stretches back thousands of years. Egyptian cubit rods dating to 3000 BCE show remarkably standardized units derived from the forearm and palm. The Roman 'mille passuum' (a thousand double paces, roughly 1,480 m) evolved into the modern mile. France launched the metric system in 1791, defining the meter as one ten-millionth of the distance from the equator to the North Pole. Although that original geodetic definition has since been superseded, it produced a remarkably accurate unit: the meter is within 0.02% of that original definition.
In everyday life, length conversion is one of the most frequent calculations people encounter. Travelers crossing between metric and imperial countries need to mentally convert road distances and speed limits. Architects and engineers in the US work in feet and inches while communicating specifications globally in millimeters. Manufacturers exporting to international markets must specify tolerances in both systems. Understanding how to move fluently between millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles is a practical skill that spans construction, medicine, athletics, and navigation.
Common Length Conversions
| From | To |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 30.48 cm |
| 1 yard | 0.9144 m |
| 1 mile | 1.609344 km |
| 1 km | 0.621371 miles |
| 1 m | 3.28084 feet |
| 1 cm | 0.393701 inches |
| 1 mm | 0.0393701 inches |
| 1 nautical mile | 1.852 km |
| 1 light year | 9.461 × 10¹² km |
| 100 m | 328.084 feet |
| 5 miles | 8.04672 km |
| 1 m | 100 cm = 1,000 mm |
| 1 km | 1,000 m = 100,000 cm |
| 1 foot | 12 inches = 30.48 cm |
Frequently Asked Questions
There are exactly 5,280 feet in one mile. This number comes from the fact that one mile was defined as 8 furlongs, and one furlong is 660 feet (originally 40 rods of 16.5 feet each).
Exactly 2.54 centimeters equal one inch. This is an internationally defined exact value set by the 1959 International Yard and Pound Agreement.
There are exactly 1,000 meters in one kilometer. The prefix 'kilo-' always means 1,000 in the SI system.
A nautical mile (1,852 m) is based on the Earth's circumference — one minute of arc of latitude — and is used in maritime and aviation navigation. A statute (regular) mile is 1,609.344 m. One nautical mile equals about 1.151 statute miles.
There are exactly 36 inches in one yard (3 feet × 12 inches per foot). Fabric, sports fields, and some construction measurements still use yards and inches in the United States.
A yard is slightly shorter than a meter: 1 yard = 0.9144 m. Conversely, 1 meter ≈ 1.094 yards. Both are roughly the distance of a large human stride. The meter is metric; the yard is imperial.
The US adopted customary units long before the metric system existed, and the cost and disruption of converting road signs, vehicles, maps, and consumer habits has kept the transition stalled. A 1975 Metric Conversion Act allowed voluntary adoption, but no deadline was set. Canada completed a full switch to metric in the 1970s–80s; the US has not.
One foot equals exactly 30.48 centimeters (12 inches × 2.54 cm/inch). A 6-foot-tall person is therefore approximately 182.88 cm or 1.83 m tall.