Scottish physicist William Thomson, knighted as Lord Kelvin, (1824-1907), devised his absolute temperature scale based on the Celsius scale. The size of a Kelvin is the same as the size of a degree Celsius. Kelvin's experimentation with heat and gases led him to devise this scale that starts with absolute zero. This scale was needed to make gas law calculations.

• All gas laws are either direct or inverse proportions.
• For a calculation of a proportion to be accurate, zero must mean nothing.
• In relative temperature scales, zero degrees is a real temperature.
• In the absolute scale that Lord Kelvin invented, zero meant no temperature. This scale could be used to make calculations about properties of gases.

Since temperature is often measured in the Celsius scale, scientists must make conversions between Kelvin and Celsius. Kelvin measurements are not called degrees like measurements in relative scales.

On the Kelvin scale:

• There are no negative temperatures.
• Absolute zero is 0 K.
• Normal body temperature is 310 K.
• Water (at sea level air pressure) freezes at 273 K.
• Water (at sea level air pressure) boils at 373 K.