Conversion formulas
°F = °C × 9/5 + 32 °C = (°F − 32) × 5/9 K = °C + 273.15 °R = °F + 459.67 = K × 9/5
Kelvin and Rankine are absolute scales: they start at absolute zero. A kelvin is the same size as a Celsius degree, and a Rankine degree is the same size as a Fahrenheit degree.
Converting by hand
Here's 350 °F, a common baking temperature, converted to Celsius and Kelvin:
- Subtract 32: 350 − 32 = 318.
- Multiply by 5/9: 318 × 5 ÷ 9 = 176.67 °C.
- Add 273.15 for Kelvin: 176.67 + 273.15 = 449.82 K.
For Celsius to Fahrenheit, do it in reverse order: multiply by 9/5 (1.8) first, then add 32. Adding 32 before multiplying is the most common error and gives a badly wrong answer.
Reference points
- Absolute zero: 0 K = −273.15 °C = −459.67 °F
- Water freezes: 0 °C = 32 °F = 273.15 K
- Normal body temperature: about 37 °C = 98.6 °F
- Water boils (at sea-level pressure): 100 °C = 212 °F = 373.15 K
- −40 is the same on the Celsius and Fahrenheit scales
Oven temperatures
| Celsius | Exact Fahrenheit | Fahrenheit | Exact Celsius |
|---|---|---|---|
| 150 °C | 302 °F | 300 °F | 148.89 °C |
| 160 °C | 320 °F | 325 °F | 162.78 °C |
| 180 °C | 356 °F | 350 °F | 176.67 °C |
| 190 °C | 374 °F | 375 °F | 190.56 °C |
| 200 °C | 392 °F | 400 °F | 204.44 °C |
| 220 °C | 428 °F | 425 °F | 218.33 °C |
| 230 °C | 446 °F | 450 °F | 232.22 °C |
Recipes usually round to the nearest setting on the dial, so 180 °C is printed as 350 °F even though the exact figure is 356 °F. For most baking that small gap doesn't matter.
Weather and body temperature
| Celsius | Fahrenheit | Celsius | Fahrenheit |
|---|---|---|---|
| −20 °C | −4 °F | 20 °C | 68 °F |
| −10 °C | 14 °F | 25 °C | 77 °F |
| 0 °C | 32 °F | 30 °C | 86 °F |
| 5 °C | 41 °F | 35 °C | 95 °F |
| 10 °C | 50 °F | 37 °C | 98.6 °F |
| 15 °C | 59 °F | 40 °C | 104 °F |
For body temperature, 38 °C is 100.4 °F, 38.5 °C is 101.3 °F and 39 °C is 102.2 °F. Each 0.5 °C step is 0.9 °F.
Converting a temperature change
The formulas above convert a reading on a thermometer. A difference between two readings converts without the 32: a rise of 10 °C is a rise of 18 °F, because only the 9/5 scale factor applies. The converter handles readings, so for a change in temperature multiply by 1.8 (°C to °F) or by 5/9 (°F to °C) yourself.