Convert any physical measurement — length, mass, volume, temperature, area, speed, pressure, energy, time, data storage & transfer rate, power, frequency, force, fuel economy (mpg/L per 100 km), angle. Auto-detects the category, handles US/imperial ambiguity, reports assumptions. Accepts natural-language queries ("what is 5 km in miles") and volume↔mass via density/substance. Deterministic and instant.