Celsius to Fahrenheit: How the Conversion Works
Last updated 2026-09-11
Celsius and Fahrenheit don't share a zero point, which is why converting between them needs both a multiplication and an offset — not just a simple ratio like most unit conversions.
Celsius to Fahrenheit
°F = (°C × 9/5) + 32. So 0°C = 32°F, and 100°C = 212°F.
Fahrenheit to Celsius
°C = (°F − 32) × 5/9.
Quick mental estimate
Double the Celsius value and add 30 for a rough Fahrenheit estimate — it's close enough for everyday use, though not exact.
Example
20°C converts to (20 × 9/5) + 32 = 68°F.
Important Considerations
- Unlike length or weight conversions, temperature scales (except Kelvin, which starts at absolute zero) have different zero points, so a simple multiplier alone won't work.
- Kelvin uses the same size "degree" as Celsius, just offset by 273.15 — no multiplication needed, only addition.
Frequently Asked Questions
- Why isn't temperature conversion just a multiplication like other units?
- Because Celsius and Fahrenheit place their zero points at different physical temperatures (0°C = 32°F), so an offset (+32 or −32) is required in addition to the scaling factor.
- What's the mental-math shortcut for Celsius to Fahrenheit?
- Double the Celsius number and add 30 — it's not exact, but it's close enough for a quick everyday estimate.