Seven categories are supported: length (km, m, cm, mm, mile, yard, foot, inch, Chinese li), weight (t, kg, g, mg, lb, oz, jin, liang), temperature, area (km², m², hectare, mu, acre, ft²), volume (m³, L, mL, US gallon, quart, ft³, in³), speed (m/s, km/h, mph, knot, ft/s) and data storage. Non-temperature units convert through an exact base-unit ratio (e.g. 1 mile = 1609.344 m, 1 lb = 0.45359237 kg); temperature uses the formulas F = C×9/5+32 and K = C+273.15.
Data storage distinguishes decimal and binary prefixes: KB/MB/GB/TB use powers of 1000 (SI), while KiB/MiB/GiB/TiB use powers of 1024 (IEC) — the reason a "1 TB" drive shows about 931 GiB in your OS. All math runs locally in your browser; nothing is uploaded.