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Free online Celsius to Fahrenheit calculator

Celsius and Fahrenheit are two ways to measure temperature. This calculator converts between them (and Kelvin) instantly.

Celsius
—
°C
Fahrenheit
—
°F
Kelvin
—
K
Common reference points
About this calculator

How to use

  1. Enter the temperature you want to convert.
  2. Select the source unit (°C, °F, or K).
  3. The result in all three units appears instantly.
  4. Scroll down for a table of common reference temperatures.

The formulas

Celsius → Fahrenheit: F = C × 9/5 + 32

Fahrenheit → Celsius: C = (F − 32) × 5/9

Celsius → Kelvin: K = C + 273.15

Kelvin → Celsius: C = K − 273.15

Common reference points

Temperature°C°FK
Absolute zero−273.15−459.670
Water freezes032273.15
Room temperature2068293.15
Body temperature3798.6310.15
Water boils100212373.15

Notes

  • Source: NIST temperature definitions and SI unit standards.
  • Results are rounded to 4 decimal places to avoid floating-point noise.
  • The Kelvin scale has no negative values — temperatures below 0 K are physically impossible.

Frequently asked

How do you convert Celsius to Fahrenheit?
F = C × 9/5 + 32. Example: 100°C = 100 × 1.8 + 32 = 212°F (boiling point of water).
How do you convert Fahrenheit to Celsius?
C = (F − 32) × 5/9. Example: 98.6°F = (98.6 − 32) × 5/9 = 37°C (normal body temperature).
How do you convert Celsius to Kelvin?
K = C + 273.15. Kelvin uses the same scale increment as Celsius but starts at absolute zero (−273.15°C). Example: 0°C = 273.15 K.
At what temperature are Celsius and Fahrenheit equal?
−40°. At −40°C = −40°F, the two scales intersect. This is because the offset (32) and scale factor (9/5) produce the same value at that point.
What is absolute zero in all three scales?
Absolute zero is 0 K = −273.15°C = −459.67°F. It is the theoretical temperature at which all thermal motion ceases.