How this works
The two scales don't share a zero point — Celsius freezes water at 0, Fahrenheit at 32 — and Fahrenheit's degree size is smaller (a Fahrenheit degree is 5/9 of a Celsius degree). Convert with °F = °C × 9/5 + 32. Useful when reading US weather forecasts, oven temperatures from American recipes, or fever thresholds in a US medical guide.
The formula
For mental conversion, "double the °C and add 30" gets you within ~2 °F across normal weather temperatures: 20 °C → ~70 °F (actual 68), 30 °C → ~90 °F (actual 86). Useful anchors: −40 °C = −40 °F (the only point where the two scales meet), 0 °C = 32 °F, 100 °C = 212 °F (water boils), 37 °C ≈ 98.6 °F (body temperature).
Example calculation
- −10 °C = 14 °F (cold snap)
- 0 °C = 32 °F (water freezes)
- 20 °C = 68 °F (room temperature)
- 180 °C = 356 °F (typical baking oven)
Frequently asked questions
Why is body temperature 98.6 °F such an oddly specific number?
It's a conversion artefact. The original 19th-century measurement gave 37 °C as average body temperature, which converts to exactly 98.6 °F (37 × 9/5 + 32 = 98.6). The "98.6" is just 37 × 1.8 + 32 expressed in °F. More recent studies suggest average healthy body temperature is closer to 36.6 °C / 97.9 °F, but the older figure remains widely quoted.
My oven only shows °F — what do I set for 200 °C?
200 × 9/5 + 32 = 392 °F. Most US ovens go in 25 °F steps, so 400 °F is the closest setting (≈ 204 °C — close enough for any non-precision baking). Common conversions: 160 °C ≈ 325 °F, 180 °C ≈ 350 °F, 200 °C ≈ 400 °F, 220 °C ≈ 425 °F.