Length Converter (General)

Using the SI-defined exact conversion factors. For example, 1 inch is defined as exactly 25.4 mm, making all imperial-to-metric conversions exact.

Historical development led to separate measurement systems. The metric system originated in France (1799), while imperial units evolved from English traditions. Most countries now use SI, but the US, UK, and a few others retain customary units.

Metric prefixes are powers of 10: kilo = 1000, centi = 1/100, milli = 1/1000. So 1 km = 1000 m, 1 cm = 0.01 m, 1 mm = 0.001 m.

No. A nautical mile (1852 m) is about 15% longer than a statute mile (1609.344 m). Nautical miles are based on Earth's circumference.

The international foot is exactly 0.3048 m. The US survey foot was 1200/3937 m (≈0.304800609 m). The US officially retired the survey foot in 2023.

All conversions use exact international definitions. The results are accurate to the full precision of floating-point arithmetic (about 15-16 significant digits).

The Planck length (~1.6×10⁻³⁵ m) is the theoretical smallest meaningful length. Practically, atomic-scale measurements use angstroms (10⁻¹⁰ m) or nanometers (10⁻⁹ m).

Since 1983, the meter is defined as the distance light travels in 1/299,792,458 of a second. This ties length to a fundamental physical constant, ensuring universal reproducibility.

Area units are length² (so multiply conversion factor by itself). Volume units are length³. For example, 1 m² = 10.764 ft², and 1 m³ = 35.315 ft³.