Utiliki

Temperature Converters

6 converters, all running in your browser.

Temperature is the one category on this site where conversion is not a multiplication. Every other unit shares a zero point, so converting means scaling. Celsius and Fahrenheit do not: their zeros are different physical temperatures, so the conversion needs an offset as well.

`` °F = °C × 9/5 + 32 °C = (°F − 32) × 5/9 K = °C + 273.15 ``

That is why you cannot convert a temperature *difference* the same way you convert a temperature. A rise of 10 °C is a rise of 18 °F, not 50 °F — for a difference you apply the ratio and drop the offset entirely.

Kelvin is the SI base unit and starts at absolute zero, so it needs no offset relative to Celsius beyond the fixed 273.15, and there is no such thing as a negative kelvin. The scales cross at −40, which is the same temperature in Celsius and Fahrenheit and a useful thing to remember when checking whether a conversion is the right way round.

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Reference Points Worth Knowing

Point°C°FK
Absolute zero−273.15−459.670
Where the scales cross−40−40233.15
Water freezes032273.15
Comfortable room2170294.15
Body temperature3798.6310.15
Water boils at sea level100212373.15
Domestic oven, moderate180356453.15
The −40 crossing is the most useful of these as a sanity check: if a conversion puts a Fahrenheit value on the wrong side of its Celsius value relative to −40, the formula was applied backwards.

Mental Approximations

The exact conversion is ×9/5 + 32, which is awkward in your head. Two shortcuts get close:

  • Celsius to Fahrenheit: double it and add 30. At 20 °C that gives 70 against a true 68 —
within 2 degrees across the whole range people actually experience.
  • Fahrenheit to Celsius: subtract 30 and halve. At 70 °F that gives 20 against a true 21.1.
Both drift at extremes and are entirely adequate for weather.

Why Oven Temperatures Are Not Exact

Recipe temperatures are conventional rather than converted. A "moderate" oven is 180 °C in Europe and 350 °F in the US, and 180 °C is actually 356 °F — the numbers were each rounded to something memorable in their own scale. Converting a recipe precisely produces figures like 177 °C that no oven dial has, and the 4-degree difference changes nothing.

Boiling Point Moves With Altitude

Water boils at 100 °C only at sea level. It drops roughly 1 °C every 300 metres, so at 2,000 m it boils at about 93 °C — which is why high-altitude cooking takes longer and why pressure cookers exist.

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