Length Converter

1 inch = 2.54 cm exactly (set by international agreement in 1959). From that: 1 foot = 30.48 cm, 1 meter = 39.37 inches = 3.28 feet. A person 6 feet tall is 182.9 cm. For a quick estimate, multiply inches by 2.5 to get centimeters (slightly low but close). A standard interior door is 80 inches tall, which equals about 203 cm.

1 mile = 1.60934 km; 1 km = 0.6214 miles. A quick mental estimate: multiply miles by 1.6 for km. Practical benchmarks: a 5K race = 3.107 miles; a marathon is 42.195 km = 26.22 miles. The US, Liberia, and Myanmar use miles for road distances; virtually everywhere else uses kilometers. Speed limit signs and odometers differ between these systems.

10 mm = 1 cm; 100 cm = 1 m; 1,000 m = 1 km. Everyday references: a dime is about 1 mm thick; a standard 12-inch ruler is 30 cm (roughly 1 foot); a 100-meter dash is about the length of a football field including end zones; 1 km is a 10-12 minute walk at an average pace. These anchors make it easy to sanity-check any metric length conversion.

1 nautical mile = 1.852 km = 1.151 statute (land) miles. It is defined as 1 minute of arc of latitude on Earth's surface, which makes navigation math straightforward. Speed at sea and in aviation is measured in knots (1 knot = 1 nautical mile per hour). A commercial airliner cruising at 500 knots is traveling about 575 mph (926 km/h).