# What temperature scale starts at absolute zero?

May 13, 2014

Two temperature scales start at absolute zero — the Kelvin scale and the Rankine scale.

Absolute zero is the lowest possible temperature. Nothing could be colder, and particles are at their lowest possible energy levels.

On the Celsius scale, absolute zero is -273.15 °C, and the freezing point of water is 0 °C.

On the Kelvin scale, absolute zero is defined as 0 K. The other defining point is the triple point of water.

The solid, liquid, and gaseous phases of water can exist in equilibrium at 273.16 °C. The kelvin is defined as $\frac{1}{273.16}$ of the triple point temperature.

This makes one kelvin the same size as one Celsius degree, so the freezing point of water is 273.15 K. The conversion formula is K = C + 273.15°.

Most scientists worldwide use the Kelvin scale.

The Rankine scale also starts at absolute zero. It is like the Kelvin scale, but its degrees are the same size as a Fahrenheit degree.

On the Fahrenheit scale, absolute zero is -459.67 °F. The conversion formula is R = F + 459.67.

Many engineers use the Rankine scale.

Here is a comparison of the four temperature scales. 