Temperature Converter: Celsius, Fahrenheit and Kelvin

Temperature formulas

°F = °C × 9/5 + 32 °C = (°F − 32) × 5/9 K = °C + 273.15

Unlike length or weight, temperature scales do not share a zero point, so you cannot convert by multiplying alone. First remove the offset, then scale. A degree Fahrenheit is 5/9 the size of a degree Celsius, and a kelvin is the same size as a degree Celsius.

Example: 20 °C to Fahrenheit is 20 × 9/5 + 32 = 36 + 32 = 68 °F. Back again: (68 − 32) × 5/9 = 36 × 5/9 = 20 °C.

Reference temperatures

Reference temperatures in all three scales
Reference point	Celsius	Fahrenheit	Kelvin
Absolute zero	-273.15 °C	-459.67 °F	0 K
Celsius and Fahrenheit are equal	-40 °C	-40 °F	233.15 K
Freezing point of water	0 °C	32 °F	273.15 K
Mild room temperature	20 °C	68 °F	293.15 K
Typical human body temperature (approx.)	37 °C	98.6 °F	310.15 K
Boiling point of water at sea-level pressure	100 °C	212 °F	373.15 K
Moderate oven	180 °C	356 °F	453.15 K

Water boils at 100 °C only at standard sea-level pressure; at altitude it boils at a lower temperature. Normal body temperature varies between people and through the day, so 37 °C is a typical value, not a precise threshold.

Temperature differences are converted differently

If a forecast says it will be 10 degrees warmer, that is a change, not a temperature. A change of 10 °C equals a change of 18 °F (multiply by 9/5 without adding 32), and a change of 10 K. This converter converts temperatures (readings), so use the 9/5 factor alone for differences.

Who uses which scale?

Celsius is used for weather and everyday temperatures in nearly every country. The United States and a few other places use Fahrenheit for weather, cooking and body temperature. Kelvin is the SI unit of temperature, used in science and engineering; it is written without the degree sign (300 K, not 300 °K).

Common questions

Is there a quick way to convert in my head?

Double the Celsius figure and add 30 for a rough Fahrenheit value (20 °C → 70 °F; exact 68 °F). The shortcut drifts at extremes: at 40 °C it gives 110 °F instead of 104 °F.

Why can’t I enter a temperature below absolute zero?

Absolute zero (0 K, −273.15 °C, −459.67 °F) is the lowest temperature possible, so values below it are not physical temperatures. If you meant a temperature difference, see the section above.