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Temperature converter

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For temperature readings. Decimals: 12.5 or 12,5, without thousands separators.

How temperature conversion works

Enter a temperature reading and select its current scale and the scale you need. Celsius, Fahrenheit and Kelvin use different zero points, so converting a reading can require both multiplication and an offset. Swap exchanges the scales while keeping the number you entered.

Celsius and Fahrenheit readings

A Celsius degree is 1.8 times the size of a Fahrenheit degree. The scales also have different zero points, which is why you add or subtract 32 when converting a reading.

°F = °C × 9 ÷ 5 + 32; °C = (°F − 32) × 5 ÷ 9

  1. To convert Celsius to Fahrenheit, multiply by 1.8 and add 32.
  2. To convert Fahrenheit to Celsius, subtract 32 and divide by 1.8.
  3. The number −40 is the same reading on both scales.

20 °C equals 68 °F. A reading of 98.6 °F equals 37 °C.

Kelvin and absolute zero

The kelvin has the same interval size as the Celsius degree, but its zero is absolute zero. Kelvin uses K without a degree sign. This converter accepts ordinary temperature readings at or above absolute zero.

K = °C + 273.15; °C = K − 273.15

  1. Add 273.15 to a Celsius reading to get kelvin.
  2. Subtract 273.15 from a kelvin reading to get Celsius.
  3. Values below 0 K, −273.15 °C or −459.67 °F are rejected.

0 °C equals 273.15 K. Absolute zero is 0 K, which equals −273.15 °C and −459.67 °F.

Precision and temperature changes

The result uses the maximum decimal places set under Options. The ≈ symbol marks a rounded display. The conversion constants and intermediate arithmetic remain exact. This tool converts readings, not temperature differences.

A change of 10 °C = A change of 10 K = A change of 18 °F

  1. Increase precision when a Fahrenheit-to-Celsius result repeats.
  2. Copy takes the number at the precision currently displayed.
  3. For a change or interval, do not add the 32 or 273.15 zero-point offsets.

A reading of 10 °C is 50 °F. A rise of 10 Celsius degrees is a rise of 18 Fahrenheit degrees. Those are different calculations.

Definitions: NIST temperature conversion