Two scales, one temperature
Most of the world measures temperature in degrees Celsius, while the United States uses Fahrenheit for weather, cooking and body temperature. Recipes, oven dials, travel forecasts and science homework all call for switching between them.
This Celsius to Fahrenheit converter works both ways, shows the result in kelvin as well, and gives a quick mental shortcut beside the exact answer so you can sanity check it in your head.
How to use it
- Choose °C to °F or °F to °C.
- Type the temperature. Negative numbers are fine.
- Read the converted temperature, then the kelvin value and the quick estimate.
- Open the working to see each step of the formula.
The conversion formulas
°F = °C × 9 ÷ 5 + 32
°C = (°F − 32) × 5 ÷ 9
K = °C + 273.15Water freezes at 0 °C, which is 32 °F, and boils at 100 °C at sea level, which is 212 °F. So 100 Celsius degrees span the same range as 180 Fahrenheit degrees, which is where 9 ÷ 5 comes from. Kelvin uses the same size of degree as Celsius but starts at absolute zero, so the two differ by exactly 273.15.
Worked example: 25 °C
- Multiply by 9 ÷ 5: 25 × 1.8 = 45
- Add 32: 45 + 32 = 77 °F
- In kelvin: 25 + 273.15 = 298.15 K
A warm day of 25 °C is 77 °F, or 298.15 K. The quick estimate, doubling and adding 30, gives 80 °F, close enough to judge the weather.
Common temperatures
| °C | °F | For example |
|---|---|---|
| −40 | −40 | Where the scales meet |
| −20 | −4 | A hard winter day |
| 0 | 32 | Water freezes |
| 10 | 50 | A cool day |
| 20 | 68 | Room temperature |
| 30 | 86 | A hot day |
| 37 | 98.6 | Typical body temperature |
| 100 | 212 | Water boils at sea level |
Oven settings follow the same rule: 180 °C is 356 °F, usually set as 350 °F, and 200 °C is 392 °F, usually set as 400 °F.
Where the two scales came from
Daniel Gabriel Fahrenheit built his scale in the early 1700s, and Anders Celsius proposed his in 1742. The Celsius scale ties its two fixed points to water, 0 for freezing and 100 for boiling, which makes it easy to use in science and everyday life. Fahrenheit has smaller degrees, so a change of 1 °C is a change of 1.8 °F. That is why weather forecasts in Fahrenheit move in bigger numbers for the same change in the air.
Kelvin is the scale science uses for absolute temperature. It has no negative values and no degree sign: 300 K, not 300 °K.
Quick tricks
- °C to °F in your head: double it and add 30. It is closest between about 0 and 20 °C.
- °F to °C in your head: take away 30 and halve it.
- Remember a few anchors: 10 °C is 50 °F, 20 °C is 68 °F, 30 °C is 86 °F.
- For other units, the unit converter covers length, weight, volume and more.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9, divide by 5, then add 32. For 20 °C, that is 20 × 1.8 = 36, plus 32, which gives 68 °F. For a quick estimate in your head, double the Celsius figure and add 30, which gives 70 °F.
How do I convert Fahrenheit to Celsius?
Take away 32, then multiply by 5 and divide by 9. For 98.6 °F, that is 66.6 × 5 ÷ 9 = 37 °C. In your head, take away 30 and halve the result: 98.6 becomes about 34, a rough but quick guide that runs low at higher temperatures.
At what temperature are Celsius and Fahrenheit the same?
At −40 degrees. Put −40 into either formula and you get −40 back. Above that point, a Fahrenheit reading is always the higher number; below it, the Fahrenheit reading is the lower one. It is a handy anchor for checking any conversion.
What is absolute zero in Celsius and Fahrenheit?
Absolute zero, the coldest possible temperature, is 0 kelvin, which is −273.15 °C or −459.67 °F. Nothing can be colder, so the converter flags any temperature below it. Kelvin starts at absolute zero, which is why scientists use it for many calculations.
Related calculators
More free tools from CloveDesk
CloveDesk gives freelancers and small teams one place for quotes, e-signatures, invoices, files and a portal for each client.
Last updated: