The exact equivalent
Subtract 273.15. The two scales use degrees of exactly the same size, so there is no factor at all: only the offset differs.
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 Celsius are a smaller unit than kelvin, the number has to come out bigger. If it comes out smaller, you divided when you should have multiplied.
Conversion table
| K | °C |
|---|---|
| 1 | -272.15 |
| 2 | -271.15 |
| 5 | -268.15 |
| 10 | -263.15 |
| 20 | -253.15 |
| 50 | -223.15 |
| 100 | -173.15 |
Reference points to picture it
| Reference | Equals |
|---|---|
| Absolute zero | 0 K = −273.15 °C |
| Water freezes | 273.15 K = 0 °C |
| Room temperature | 293 K = 19.9 °C |
| Water boils | 373.15 K = 100 °C |
The trick for doing it in your head
Subtract 273. The extra 0.15 rarely matters outside a laboratory, and it is easy to add back if it does.
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.