# What is the Celsius temperature scale?

May 14, 2014

The Celsius scale is a temperature scale in which the freezing and boiling points of water are exactly 0 °C and 100 °C. There are 100 equal degrees between these two temperatures.

These temperatures do not define the Celsius scale. International agreement defines the reference points as absolute zero and the triple point temperature of specially purified water.

The triple point of water is the temperature at which solid, liquid, and gaseous water can exist at equilibrium.

Absolute zero, the lowest temperature possible, is exactly −273.15 °C. The triple point temperature of water is exactly 0.01 °C.

The difference between these two temperatures is 273.16 °C. A Celsius degree is exactly $\frac{1}{273.16}$ of this difference.

This definition keeps the freezing point of water at exactly 0 °C and the boiling point of water at exactly 100 °C.