What are the formulas between Celsius, Fahrenheit, and Kelvin?

Fahrenheit equals Celsius times 9/5 plus 32. Kelvin equals Celsius plus 273.15. To go from Fahrenheit to Celsius, subtract 32 then multiply by 5/9. Kelvin has no negative values because it starts at absolute zero, the coldest possible temperature.

Why is absolute zero important?

Absolute zero, at 0 Kelvin, minus 273.15 Celsius, or minus 459.67 Fahrenheit, is the theoretical point where particle motion reaches its minimum and thermal energy is at its lowest. It anchors the Kelvin scale and is unreachable in practice, though labs have come within billionths of a degree.

What counts as normal body temperature?

The traditional figure is 37 Celsius, or 98.6 Fahrenheit, though healthy adults range from about 36.1 to 37.2 Celsius and vary through the day. Modern studies suggest the average is slightly below the classic 37 figure, closer to 36.6 Celsius.

What is standard room temperature?

Comfortable indoor room temperature is usually defined as about 20 to 22 Celsius, or 68 to 72 Fahrenheit. Scientific standard ambient temperature is often taken as 25 Celsius (298.15 Kelvin) for reporting measurements.

Does water always boil at 100 Celsius?

Only at standard sea-level pressure. Boiling point drops with altitude as air pressure falls — water boils near 93 Celsius at 2000 metres. The 100 Celsius figure is defined at one standard atmosphere of pressure.

Temperature Reference Points

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Some temperatures come up again and again — the freezing and boiling points of water, body temperature, absolute zero, room temperature. This reference lists each landmark in all three common scales (Celsius, Fahrenheit, Kelvin) and lets you convert any custom value into the same three units.

How it works

The three scales are linear transformations of one another. The conversions used throughout this tool are:

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

Kelvin is an absolute scale anchored at 0 K = absolute zero = −273.15 °C, so it never goes negative. Each reference point is stored in Celsius and converted on the fly to Fahrenheit and Kelvin for display.

Notable landmarks

Absolute zero — 0 K, the coldest possible temperature.
Water freezes — 0 °C / 32 °F, at standard pressure.
Room temperature — about 20–22 °C, comfortable indoors.
Body temperature — about 37 °C / 98.6 °F.
Water boils — 100 °C / 212 °F, at one standard atmosphere.

These anchor everyday intuition: if you know that 37 °C is body heat and 100 °C is boiling water, you can quickly judge any Celsius reading in between.