Convert between Celsius, Fahrenheit, and Kelvin. Temperature conversion isn’t a simple multiplication like most units — it needs an offset as well as a scale factor, which is exactly what this calculator handles for you.
Quick reference
- 0°C = 32°F = 273.15 K (water freezes)
- 100°C = 212°F = 373.15 K (water boils)
- 37°C = 98.6°F (average body temperature)
- -40°C = -40°F (the one point they match)
Celsius to Fahrenheit trips up more people than almost any other conversion because the formula isn’t a straight multiplication — there’s an offset involved. If you want to do it by hand: Fahrenheit = (Celsius × 9/5) + 32.
How to convert temperature
Temperature scales have different zero points as well as different step sizes, so you need a formula rather than a single multiplier:
- Celsius to Fahrenheit: °F = °C × 9/5 + 32
- Fahrenheit to Celsius: °C = (°F − 32) × 5/9
- Celsius to Kelvin: K = °C + 273.15
Example: 25°C × 9/5 = 45, plus 32 = 77°F. For a rough mental estimate, double the Celsius figure and add 30 (25°C → 80°F).
Frequently asked questions
Why can’t I just multiply to convert temperature?
Because 0°C and 0°F are different temperatures. Water freezes at 0°C but at 32°F, so the conversion needs an offset (the +32 or −32) as well as a scale factor.
What is absolute zero?
Absolute zero is the lowest possible temperature: 0 K, which equals −273.15°C or −459.67°F.
Is Kelvin written with a degree sign?
No. Kelvin is an absolute scale, so it is written simply as K — for example 300 K, not 300°K.