Temperature
Celsius, Fahrenheit, Kelvin
Temperature is one of those measurements where three different scales are in widespread use, depending on the country and the discipline. Celsius is the global scientific standard and the everyday scale in most of the world. Fahrenheit is still used for weather and cooking in the United States. Kelvin is the SI absolute scale used in science and engineering.
This converter handles all three with formulas baked in so you do not have to remember which to use when.
What this converter handles
- Celsius ↔ Fahrenheit
- Celsius ↔ Kelvin
- Fahrenheit ↔ Kelvin
Enter any value in any of the three fields and the other two update instantly.
Conversion formulas
- Celsius to Fahrenheit:
F = C × 9/5 + 32 - Fahrenheit to Celsius:
C = (F − 32) × 5/9 - Celsius to Kelvin:
K = C + 273.15 - Kelvin to Celsius:
C = K − 273.15 - Fahrenheit to Kelvin:
K = (F − 32) × 5/9 + 273.15
Common reference points
- Water freezes: 0°C = 32°F = 273.15 K
- Comfortable room: 22°C ≈ 71.6°F
- Human body: 37°C ≈ 98.6°F
- Water boils (sea level): 100°C = 212°F = 373.15 K
- Absolute zero: 0 K = −273.15°C = −459.67°F
When to use this
Travel (checking a foreign weather forecast), cooking (recipes from another country), science homework, and any context where you need to convert quickly without doing the math in your head.
Mental shortcuts
For a quick estimate from Celsius to Fahrenheit, double the Celsius value and add 30 — it is not exact but it is close enough for weather: 20°C ≈ 70°F (actual: 68°F), 25°C ≈ 80°F (actual: 77°F). For precise values, always use the proper formula.
Frequently asked questions
Why does Kelvin not use a degree symbol?
Because Kelvin is an absolute scale defined from a fixed zero point, scientists write "K" without the degree symbol — by convention. Temperatures in Kelvin can never be negative.
What is "negative" Fahrenheit?
Fahrenheit has a zero point that does not correspond to any physical reference, so negative values are normal in cold climates. −40°F is the unique temperature where Fahrenheit and Celsius are equal.
Why 273.15 for Celsius to Kelvin?
Because absolute zero — the theoretical lowest possible temperature — is at exactly −273.15°C.