How to Convert Celsius and Fahrenheit
Temperature · Last updated: July 2025
Celsius (°C) and Fahrenheit (°F) are the two temperature scales most people encounter daily. They are linearly related but offset: water freezes at 0 °C / 32 °F and boils at 100 °C / 212 °F at standard atmospheric pressure.
The formulas
°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9
You must apply the offset (32) before or after scaling—order matters. Doubling Celsius does not double Fahrenheit.
Anchor points
| From | To |
|---|---|
| 0 °C | 32 °F (water freezes) |
| 20 °C | 68 °F (room temp) |
| 37 °C | 98.6 °F (body temp) |
| 100 °C | 212 °F (water boils) |
| −40 °C | −40 °F (same number) |
Everyday contexts
Weather
US forecasts use °F; most other countries use °C. 30 °C is a hot summer day (86 °F), not “cold” as 30 °F would be (−1 °C).
Cooking and ovens
Recipes may specify 180 °C while US ovens show °F (350 °F is roughly 177 °C). Baking is sensitive—use exact conversion, not rough estimates.
Healthcare
Fever thresholds differ by scale: 38 °C ≈ 100.4 °F. Always note which unit a device displays.
Quick estimation (not for baking)
- °C → °F: multiply by 2 and add 30 (20 °C → 70 °F; actual 68 °F).
- °F → °C: subtract 30 and divide by 2 (70 °F → 20 °C; actual 21 °C).
Common mistakes
- Forgetting to add or subtract 32 before scaling.
- Using × 2 instead of × 9/5 for “exact” work.
- Confusing temperature change (ΔT) with absolute temperature— a 10 °C rise equals an 18 °F rise, not 10 °F.
References
Convert temperature on tounits.com — try 25 C or 77 F.