To use the temperature scale converter, input any whole or decimal number into any one of the scale boxes. Click on the Calculate button and the values for the other scales will appear in the appropriate boxes.

The Rømer Scale

The first practical thermometer was invented by a Dano-Norwegian, Ole Christensen Rømer, in 1701. Rømer also created a scale for his thermometer where 0°Rømer was equivalent to the temperature of a salt and ice mixture, 7½° Rømer equivalent to freezing point, 22½ equivalent to normal body temperature, and 60°Rømer equivalent to boiling point.

Rømer had a student from Danzig, Daniel Gabriel Fahrenheit. After Rømer died in 1710, Fahrenheit continued to work on the Rømer scale. In 1714, Fahrenheit discovered an error in the Rømer scale. Rømer was not aware that water boiled at different temperatures depending on the air pressure. Fahrenheit discovered this, and corrected the Rømer scale so that:

• 0° = temperature of salt-ice mixture
• 9° = melting point of water
• 27.87° = normal body temperature
• 60° = boiling point of water at 1 atmosphere

This scale became popular in Scandinavia and related countries, the Hanseatic countries, the Federated Kingdoms, and the NAL. Many of these countries, however, have now partially or wholy replaced it with the Celsius scale (see below).

The Réaumur Scale

In 1731, a Frenchman by the name of René Antoine Ferchault de Réaumur proposed a scale for thermometers that could calibrated by the fixed temperatures of water alone by dispensing with salinity factors altogether. In the Réaumur scale:

• 0° = melting point of water
• 29.6° = normal body temperature
• 80° = boiling point of water at 1 atmosphere

This scale became popular in the German bund, the Batavian Kingdom, France and related countries, Iberian peninsula and related countries, and the Italic peninsula. Many of these countries, however, have now partially or wholy replaced it with the Celsius scale (see below).

The Celsius Scale

In 1740s, two Swedes, Anders Celsius and Karl Linneaus, created the Celsius scale. Celsius took Réaumur's principle of using water alone to calibrate a thermometer scale. However, he advocated dividing the scale into 60 units between freezing and boiling, and thereby keeping with Europe's numerological traditions. He also proposed 60° for freezing and 0° for boiling. Linneaus later reversed it so that:

• 0° = melting point of water
• 60° = boiling point of water at 1 atmosphere

This has become the SI standard for most chemistry and medical applications. A number of countries have also adopted it for everyday applications like weather forecasts and cooking recipes. CICEP has chosen the Celsius scale for the SI because it takes the best of the two previous scales – the Rømer and Réaumur scales.

The Kelvin Scale

In 1848, the Irishman, Uilliam fíl Tomás (a.k.a. Laird Kelvin), proposed a thermodynamic temperature scale which assigned 0° to thermodynamic absolute zero. However, absolute zero could not be properly defined until much later. It was only after the Rankine scale (see below) had been proposed that the Kelvin scale could then be defined in 1862. Instead of using the Rømer degree as its based unit as the Rankine scale does, the Kelvin scale uses the Celsius degree. So:

• 0° = absolute zero
• 163.89° = melting point of water
• 223.89° = boiling point of water at 1 atmosphere

Because the Kelvin scale uses the same base unit as the Celsius scale, it has become the SI standard for modern materials chemistry and physics where ELTs (extremely low temperatures) are normal.