Temperature conversion formulas
Every formula below is exact: the constants 9/5, 32, 273.15 and 459.67 are definitions, not measurements. Examples use 25 of the starting unit.
| Conversion | Formula | Example |
|---|---|---|
| Celsius to Fahrenheit | °F = °C × 9/5 + 32 | 25 °C = 77 °F |
| Celsius to Kelvin | K = °C + 273.15 | 25 °C = 298.15 K |
| Celsius to Rankine | °R = (°C + 273.15) × 9/5 | 25 °C = 536.67 °R |
| Fahrenheit to Celsius | °C = (°F − 32) × 5/9 | 25 °F = −3.89 °C |
| Fahrenheit to Kelvin | K = (°F + 459.67) × 5/9 | 25 °F = 269.26 K |
| Fahrenheit to Rankine | °R = °F + 459.67 | 25 °F = 484.67 °R |
| Kelvin to Celsius | °C = K − 273.15 | 25 K = −248.15 °C |
| Kelvin to Fahrenheit | °F = K × 9/5 − 459.67 | 25 K = −414.67 °F |
| Kelvin to Rankine | °R = K × 9/5 | 25 K = 45 °R |
| Rankine to Celsius | °C = (°R − 491.67) × 5/9 | 25 °R = −259.26 °C |
| Rankine to Fahrenheit | °F = °R − 459.67 | 25 °R = −434.67 °F |
| Rankine to Kelvin | K = °R × 5/9 | 25 °R = 13.89 K |
Step through any formula
°C = (°F − 32) × 5/9
Start with 98.6 °F on the Fahrenheit scale.
Where the constants come from
9/5 and 5/9. Between water's freezing and boiling points there are 100 Celsius degrees and 180 Fahrenheit degrees. 180/100 = 9/5 = 1.8.
32. Water freezes at 32 °F, so a Fahrenheit reading must be shifted by 32 before the degree sizes line up.
273.15. Absolute zero is 273.15 Celsius degrees below 0 °C. Kelvin uses Celsius-sized steps, so only this shift is needed.
459.67. Absolute zero is 459.67 Fahrenheit degrees below 0 °F (273.15 × 1.8 − 32), which is where Rankine starts.
Order matters
For Fahrenheit to Celsius, subtract 32 before multiplying. Multiplying first, (°F × 5/9) − 32, is a common slip: for 212 °F it gives 85.8 instead of 100.
Questions
What is the formula for Celsius to Fahrenheit?
°F = °C × 9/5 + 32 (or × 1.8 + 32).
What is the formula for Fahrenheit to Celsius?
°C = (°F − 32) × 5/9. Subtract first, then multiply.
What is the formula for Celsius to Kelvin?
K = °C + 273.15.
What is the formula for Fahrenheit to Kelvin?
K = (°F + 459.67) × 5/9.