The exact equivalent
Multiply by 1.8 and add 32. The two scales agree at exactly one point, −40, and diverge in both directions from there.
How to convert it by hand
Temperature is not converted by multiplying by a factor, because each scale puts its zero in a different place. You have to adjust the offset first and then the size of the degree.
A tip that saves mistakes: check the result goes the way you expect. If degrees Fahrenheit are a smaller unit than degrees Celsius, the number has to come out bigger. If it comes out smaller, you divided when you should have multiplied.
Conversion table
| °C | °F |
|---|---|
| 1 | 33.8 |
| 2 | 35.6 |
| 5 | 41 |
| 10 | 50 |
| 20 | 68 |
| 50 | 122 |
| 100 | 212 |
Reference points to picture it
| Reference | Equals |
|---|---|
| A cold winter day | 0 °C = 32 °F |
| Room temperature | 21 °C = 69.8 °F |
| A hot summer day | 35 °C = 95 °F |
| A moderate oven | 180 °C = 356 °F |
The trick for doing it in your head
Double it and add 30. For 20 °C that gives 70 against a true 68, and for 25 °C it gives 80 against 77 — close enough to decide what to wear, and wrong enough that you would not bake with it.
It is fine for getting by without a phone, but not for anything that depends on precision: in a recipe, on a building site or in a dose, use the exact conversion.