Converting Between Celsius, Fahrenheit, and Kelvin Correctly
Celsius to Fahrenheit: °F = °C × 9/5 + 32. Fahrenheit to Celsius: °C = (°F − 32) × 5/9. Celsius to Kelvin: K = °C + 273.15. Unlike most unit conversions, temperature conversion (between Celsius and Fahrenheit specifically) isn't a single multiplication, since the two scales don't share a common zero point.
Temperature is the one common conversion category that genuinely requires a small formula rather than a single multiplication, which is worth understanding rather than just memorizing.
Celsius to Fahrenheit, worked
20°C to Fahrenheit: 20 × 9/5 = 36, plus 32 = 68°F. The formula has two steps because Celsius and Fahrenheit have different zero points (0°C is 32°F, not 0°F) and different-sized degree intervals, which is why a straightforward multiplication alone isn't enough.
Fahrenheit to Celsius, worked
68°F to Celsius: 68 − 32 = 36, then 36 × 5/9 = 20°C — the reverse of the process above, subtracting first to account for the different zero point, then scaling for the different degree size.
Celsius to Kelvin
Converting to Kelvin is simpler — Kelvin uses the same degree size as Celsius, just shifted so that 0 K is absolute zero rather than the freezing point of water, so the conversion is a single addition: K = °C + 273.15, with no multiplication needed.