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Temperature Converter

Convert between Celsius, Fahrenheit and Kelvin instantly, with formulas and common reference points like body temperature and boiling water.

An American oven recipe is in Fahrenheit, a laboratory report in kelvin, most of the world in Celsius — three scales share the field, and a fever of 38.5 °C reads as 101 °F on a US thermometer, which is where converting by hand goes wrong. Enter any one temperature and all three come back at once, with the formulas and the usual reference points — body temperature, the freezing and boiling points of water, common oven settings — set out below.

The formulas and the pitfalls: °F = °C × 1.8 + 32, which carries an offset and so is not a plain ratio; K = °C + 273.15, with absolute zero at 0 K or −273.15 °C. A hundred degrees Fahrenheit is not a hotter version of a hundred degrees Celsius — a body temperature of 37 °C is 98.6 °F — and negative Fahrenheit temperatures are routine in a North American winter, so do not scale them by proportion in your head.

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How to use

  1. Enter the temperature in any one scale.
  2. Read the other two alongside it.
  3. Check the formula — Fahrenheit carries an offset, not just a factor.
  4. Compare against the reference points rather than estimating.

How it works

Celsius to Fahrenheit

Celsius to Fahrenheit: F = C x 9/5 + 32. For example 37 C = 98.6 F.

Celsius to Kelvin

Celsius to Kelvin: K = C + 273.15. For example 100 C = 373.15 K.

The point where the two scales meet

The two scales are equal at minus 40: -40 C = -40 F, the only point where they coincide.

Code example

JavaScript Converting between three temperature scales 

const c2f = (c) => c * 1.8 + 32;
const f2c = (f) => (f - 32) / 1.8;
const c2k = (c) => c + 273.15;

c2f(37);     // 98.6 (body temperature)
f2c(100);    // 37.78
c2k(-273.15);// 0 (absolute zero)

Python The same formulas in Python 

c2f = lambda c: c * 1.8 + 32
f2c = lambda f: (f - 32) / 1.8

[(c, c2f(c)) for c in (0, 37, 100)]
# [(0, 32.0), (37, 98.6), (100, 212.0)]

# Kelvin: K = C + 273.15; thermodynamic work always uses K

FAQ

Why does the US use Fahrenheit?

Fahrenheit was designed with the brine freezing point at 0 and body temperature around 100, giving finer everyday resolution; Celsius uses water's freezing at 0 and boiling at 100, which is more intuitive scientifically. China commonly uses Celsius.

What is a body temperature of 37 C in Fahrenheit?

37 x 9/5 + 32 = 98.6 F, the standard reference. Readings between about 97.7 and 99.5 F (36.5-37.5 C) fall within normal fluctuation.

Do Kelvin and Celsius differ by just a constant?

Yes. The Kelvin and Celsius scales share the same interval; only the zero point differs: K = C + 273.15, with 0 K (absolute zero) at -273.15 C.

How do Celsius and Fahrenheit convert?

Fahrenheit = Celsius x 9 / 5 + 32; Celsius = (Fahrenheit - 32) x 5 / 9. For example 100 C = 212 F, 37 C = 98.6 F. Remember -40 C = -40 F as a quick check that the formula isn't reversed.

How is Kelvin defined?

The kelvin (K) is the SI unit of thermodynamic temperature, with 0 K at absolute zero, about -273.15 C, so K = C + 273.15. Kelvin takes no "degree" — write 273.15 K, not 273.15 degrees K.

What temperature counts as a fever?

Common references: armpit 37.3 C or above, oral 37.5 C or above, rectal 38 C or above. Body temperature naturally varies through the day (lower in the morning, higher in the evening), and the site and method matter — judge by comparing same-site, same-method readings.

Is the feels-like temperature in forecasts the same as air temperature?

No. Air temperature is the actual temperature; feels-like also folds in humidity, wind and sunlight — high summer humidity feels muggier, strong winter wind feels much colder. This tool converts temperature units; feels-like cannot be derived directly from air temperature.