Four categories — temperature, length, weight, speed — with every unit in the active category shown as its own input row. Type into any row and all the others update simultaneously, so you can read 100°F as Celsius and Kelvin at once rather than converting pairwise.
Which factors are exact, and the one that is not
The length factors are the exact international definitions: 1 inch = 0.0254 m, 1 foot = 0.3048 m, 1 mile = 1609.344 m. Because the tool converts through meters with these exact values, derived relationships come out perfectly — enter 1 mile and the feet row reads exactly 5280, with no floating-point residue.
Weight is the exception. The tool uses 0.453592 kg per pound, a six-decimal truncation of the exact 0.45359237. The error is invisible at kitchen scale but measurable in bulk: converting 1000 kg gives 2204.6244 lb here versus the true 2204.6226 lb — about 1.8 thousandths of a pound per metric ton. Similarly the knot uses 0.514444 m/s rather than the exact 1852/3600, so 20 knots shows 37.039968 km/h instead of a clean 37.04. Fine for navigation homework; do not use it to calibrate instruments.
One naming trap: the Ton row is the metric tonne, 1000 kg. If you mean the US short ton (907.18 kg) or UK long ton (1016.05 kg), convert via pounds instead.
How results are displayed
Outputs are trimmed to 8 significant figures with trailing zeros dropped, which is why 100°F shows as 37.777778°C rather than a longer tail. Anything smaller than 0.001 switches to exponential notation with 4 decimal places: 1 millimeter in miles reads 6.2137e-7. Switching tabs clears all fields deliberately — values from one quantity type have no meaning in another.
Questions people ask
Why does it accept temperatures below absolute zero?
There is no physical-range validation. Enter -300 in the Celsius row and the Kelvin row will dutifully report -26.85 K, which cannot exist. The tool is a pure arithmetic layer; sanity-checking the physics is on you.
Why did all my values disappear when I changed tabs?
Tab switches reset every field on purpose. Carrying a number from the Length tab into Temperature would imply a conversion between incompatible quantities, so the tool clears state instead of guessing.
For pixel/em/rem conversions in stylesheets, the CSS units converter handles the web-specific cases this general-purpose tool does not, and the number base converter covers radix changes rather than physical quantities.