Three scales, two formulas
Celsius sets 0 at the freezing point of water and 100 at its boiling point at sea level. Fahrenheit places those at 32 and 212, so there are 180 degrees between them compared with 100 on the Celsius scale. That is where the 9/5 factor comes from, and why the 32 has to be added.
Kelvin has the same step size as Celsius but starts at absolute zero. To convert, add 273.15 to a Celsius value. Fahrenheit goes through Celsius first.
Worked examples
A fever threshold of 38°C is 38 × 1.8 + 32 = 100.4°F. A hot summer day of 95°F is (95 − 32) × 5/9 = 35°C. Liquid nitrogen boils at 77 K, which is −196.15°C or −321.07°F. An oven set to 180°C is 356°F.
Using the converter
Pick the scale you have under From and the scale you want under To, then type the value. All three scales are shown below the result so you can see the whole picture, and the reference list helps you sense how hot or cold a number is.
For other measures such as length, weight and volume, use the unit converter. This calculator is not a medical device, so for health concerns about a high temperature, follow the advice of a doctor.
Questions people ask
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (or 1.8) and add 32. So 25°C is 25 × 1.8 + 32 = 77°F. A quick estimate in your head is to double the Celsius value and add 30, which gives 80°F for 25°C, close enough for the weather.
How do I convert Fahrenheit to Celsius?
Subtract 32 and multiply by 5/9. So 98.6°F is (98.6 − 32) × 5/9 = 37°C, and 350°F is about 177°C, a common oven setting. To estimate quickly, subtract 30 and halve.
What is Kelvin used for?
Kelvin is the scientific temperature scale. It starts at absolute zero, so there are no negative values, and a step of 1 K is the same size as 1°C. Kelvin equals Celsius plus 273.15, so room temperature of 20°C is 293.15 K.
At what temperature are Celsius and Fahrenheit equal?
At −40. Setting C × 9/5 + 32 equal to C gives C = −40, so −40°C is exactly −40°F.
What is absolute zero?
Absolute zero is the lowest temperature possible: 0 K, −273.15°C or −459.67°F. At that point particles have the least possible motion. The calculator does not accept temperatures lower than that.