Temperature conversion is unique because it involves offsets, not just multiplication factors. Converting between Celsius and Fahrenheit requires both multiplication and addition.
The Three Major Temperature Scales
Celsius (°C) is used worldwide for everyday temperatures. Water freezes at 0°C and boils at 100°C. Fahrenheit (°F) is used primarily in the US, with water freezing at 32°F and boiling at 212°F. Kelvin (K) is the SI unit for science, starting at absolute zero (−273.15°C).
Conversion Formulas
- °C to °F: multiply by 9/5, then add 32
- °F to °C: subtract 32, then multiply by 5/9
- °C to K: add 273.15
- K to °C: subtract 273.15
These are exact definitions. Note: a 1°C change equals a 1 K change, but a 1°F change is only 5/9 of a degree.
Quick Mental Shortcuts
For a rough °F to °C conversion: subtract 30 and divide by 2. So 70°F → 20°C (actual: 21.1°C). For °C to °F: double and add 30. So 20°C → 70°F (actual: 68°F). Accurate within about 1–2 degrees — useful for weather.
Important References
Normal body temperature: 37°C = 98.6°F = 310.15 K. Room temperature: ~20–22°C = 68–72°F. Absolute zero: 0 K = −273.15°C = −459.67°F — the lowest possible temperature.
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