How unit conversion works
Unit conversion uses a base-unit factor map. For length, every unit is expressed in metres: a kilometre is 1,000 metres, a mile is 1,609.34 metres, a foot is 0.3048 metres. Converting from unit A to unit B means multiplying by A’s factor and dividing by B’s factor. Temperature is special-cased because Celsius and Fahrenheit have different zero points, so a simple ratio doesn’t work.
Worked examples. 1 mile = 1.609 km (1 × 1609.34 ÷ 1000). 0°C = 32°F (0 × 9/5 + 32). 1 kg = 2.205 lb (1 × 1000 ÷ 453.592).
Supported unit categories
Length — km, mi, m, ft, cm, in
Mass — kg, lb, g, oz
Volume — l, gal
Temperature — °C, °F
Why cross-category conversion fails
You can’t convert kilometres to kilograms — they measure different physical quantities. Selecting units from two different categories returns an error rather than a meaningless number.