Length Converter

Length is the most fundamental measurement in physics — the one-dimensional extent between two points. The SI base unit is the metre, defined since 1983 as the distance light travels in vacuum in 1/299,792,458 of a second (a definition that ties length to the speed of light, the most precisely measured constant in physics). Real-world length spans 60 orders of magnitude: a proton at 10⁻¹⁵ m, a bacterium at 10⁻⁶ m, a person at ~1.7 m, a car at ~5 m, a marathon at 42,195 m, a planet's orbit in AU, a galaxy in light years, the observable universe at ~93 billion light years. Converting between systems is one linear factor away — but pick the right factor: 1 ft = 0.3048 m exactly, 1 mi = 1.609344 km exactly. This Length Converter handles 15 units at once with the official factors. Need area instead? Use the Area Converter. Working with container capacity? Try the Volume Converter.