From the temperature scales that are listed here Celsius (°C), Kelvin (K), and Fahrenheit (°F) are the three scales that are in common use. The first two, Celsius and Kelvin, both belong to the metric measurement system whereas Fahrenheit belongs to the Imperial system.

The Celsius and Fahrenheit scales (and the other ones listed here) are divided into degrees where the Kelvin scale is divided into kelvins. Celsius and Kelvin are quite similar scales, one degree Celsius is the same size as one kelvin.

There are one hundred degrees between the freezing and boiling points of water on the Celsius scale and there are 100 kelvins between these two points on the Kelvin scale. They differ in where these points are assigned on the scales. Celsius uses 0 °C for the freezing point and 100 °C for the boiling point of water. On the Kelvin scale these points are 273 K for freezing and 373 K as the boiling point of water. The purpose of this is that all the values on the Kelvin scale are positive numbers. The Kelvin scale is an absolute temperature scale with 0 K at the lowest possible temperature, absolute zero. (Absolute zero is the temperature where all molecular motion has ceased.)

The Fahrenheit scale uses a smaller degree size than the previous two scales. Here there are 180 degrees between the freezing and boiling point of water. The two reference points for freezing and boiling of water on this scale are 32 °F for freezing and 212 °F for boiling of water.

Where the absolute zero point on the Kelvin scale is 0 K, it is -273 °C on the Celsius scale and -460 °F on the Fahrenheit scale.

The Rankine temperature scale uses zero as its lowest point and each degree is equivalent to one degree on the Fahrenheit scale.

The Reamur scale uses 0 for freezing and 80 for boiling of water. The point for absolute zero is set at -218.52 and the average human body temperature is 29.

• Convert Celsius to Fahrenheit and Kelvin
• Convert Fahrenheit to Celsius and Kelvin
• Convert Kelvin to Celsius and Fahrenheit