📏 Length Conversion Guide

Complete guide to length unit conversion — cm to inches, meters to feet, km to miles. Learn exact formulas, real-world use cases, and how the two measurement systems compare.

Length is the most basic of all measurements. Every civilization has needed a way to describe how far apart two things are. Today we live with two competing systems: the metric system (SI, used by 94% of the world) and imperial/customary units (US and a handful of holdouts).

The two systems: imperial vs metric

The metric system uses base-10: 1 km = 1,000 meters = 100,000 cm = 1,000,000 mm. Imperial evolved organically: 12 inches = 1 foot, 3 feet = 1 yard, 1,760 yards = 1 mile. Conversions within imperial are messy, but conversions across systems are exact.

Exact conversion factors

1 inch = 2.54 cm — exactly, since 1959
1 foot = 30.48 cm
1 mile = 1.609344 km
1 meter = 3.28084 feet
1 km = 0.621371 miles

Real-world scenarios

At the doctor's: 5'10" = 70 inches x 2.54 = 177.8 cm. Going the other way: 180 cm = 70.87 inches = 5'11".

Driving across borders: US highway 70 mph = 113 km/h. Canada uses 100 km/h ≈ 62 mph.

Real estate: A square foot is (0.3048)^2 = 0.0929 m^2, not 0.3048. This is the most common mistake. A 2,000 ft^2 home is 185.8 m^2, not 609.6 m^2.

How converters handle this

Every length unit converts through meters. Even though inches are defined relative to cm, the converters route everything through meters for consistency. You type any unit, every other unit appears instantly.