The formula
°F = °C × 9/5 + 32 — or, more memorable: multiply by 1.8 and add 32.
°C = (°F - 32) × 5/9 — subtract 32, then multiply by 5/9.
Why the weird offsets? In 1724 Fahrenheit set 0 °F as the freezing point of brine (salt water) and 96 °F as human body temperature. Anders Celsius later set 0 °C and 100 °C at water\'s freezing and boiling points — much cleaner. The two scales were never designed to be compatible.
Quick reference
- 0 °C = 32 °F (water freezes)
- 20 °C = 68 °F (room temperature)
- 37 °C = 98.6 °F (body temperature)
- 100 °C = 212 °F (water boils at sea level)
- -40 °C = -40 °F (the scales meet)
For oven temperatures
Recipe ovens often have a third notation: gas mark (UK). Use the dedicated oven temperature tool for °F ↔ °C ↔ gas mark with verbal labels like "moderate" or "hot oven".
FAQ
What is the formula for Celsius to Fahrenheit? °F = °C × 9/5 + 32. Or simpler: multiply by 1.8 and add 32. So 20 °C × 1.8 = 36, + 32 = 68 °F. Reverse: °C = (°F - 32) × 5/9.
At what temperature do Celsius and Fahrenheit read the same? -40 °C = -40 °F. The scales meet at exactly -40 — a useful party fact and the only point where both readings are identical.
Why is human body temperature 98.6 °F but 37 °C? Both are correct. 37 °C × 9/5 + 32 = 98.6 °F exactly. The "98.6 °F" figure comes from 19th-century studies; modern medicine considers the normal range 36.1–37.2 °C (97–99 °F).
Why does the US use Fahrenheit? The Fahrenheit scale (Daniel Fahrenheit, 1724) was the first standardized temperature scale and dominated English-speaking science for 200 years. The US never officially switched to Celsius. Most other countries adopted Celsius via the metric system in the 1800s–1900s.
Is Kelvin the same as Celsius? They use the same step size, but offset by 273.15. So 0 K = -273.15 °C (absolute zero), and 0 °C = 273.15 K (water freezes). 100 °C = 373.15 K (water boils). For everyday temperatures, just add 273.15 to °C to get K.
My weather app shows different temperatures for the same place — why? Likely a unit mismatch (°C vs °F) between apps, or "feels like" temperature using wind chill or humidity. Always check the unit label. For US travelers in metric countries, this is a common source of confusion.