Temperature can be defined as a measure of hotness or coldness – or, in the words of the Understanding Global Change guide of the University of California Museum of Paleontology, “the measure of the average heat or thermal energy in a substance.”

This measure is expressed in terms of what is known as a “temperature scale”. The three most common temperature scales are Celsius, Fahrenheit, and Kelvin.

Who Needs to Be Well-Versed in Temperature Scales?

For a wide range of people and industries – from scientists and engineers to medical professionals and chefs – it is often necessary to know and understand temperature scales and how to convert between them.

Here are a few examples of how various individuals and sectors may use temperature scales:

• Scientists in fields such as physics and chemistry often depend on the Kelvin scale for precise calculations and thermodynamic studies
• Engineers turn to temperature scales to help them understand the behaviours of materials, as well as to design structures that can withstand changes in temperature
• Medical professionals frequently use the Celsius scale, particularly for the measurement of body temperature
• Chefs need to understand temperature to help them prepare food properly, with scales like Celsius and Fahrenheit playing key roles
• Meteorologists depend on temperature scales to help them communicate weather conditions to the public
• The public can more easily comprehend what certain temperature readings mean – such as in weather forecasts – if they are familiar with both Celsius and Fahrenheit.

Most Common Temperature Scales

Here is your quick guide to the three temperature scales you are likeliest to need to understand, where Kelvin(k) is the base unit of temperature while the others are SI derived units .

Celsius (°C)

Part of the metric system and particularly strongly associated with weather forecasts and other “everyday” temperature readings, the Celsius scale sets the freezing point of water at 0 °C and the boiling point at 100 °C.

The Celsius scale, formerly often referred to as the “centigrade” scale, is used in most countries around the world.

Fahrenheit (°F)

Seeing its primary use in the United States while the majority of other countries use the Celsius scale, the Fahrenheit scale places water’s freezing point at 32°F and the boiling point at 212°F under standard atmospheric pressure.

Part of the imperial system, the Fahrenheit scale was the creation of physicist Daniel Gabriel Fahrenheit (1686-1736).

Kelvin (K)

Kelvin is an absolute temperature scale – in other words, it has no negative values. So, 0 K is absolute zero, representing the theoretical point where molecular motion ceases.

Developed by William Thomson, 1^st Baron Kelvin (1824-1907) during the 19^th century, this scale sees widespread use in scientific and engineering fields, particularly in relation to thermodynamic calculations.

Conversion Between Different Temperature Scales

To convert between temperature scales, you can simply use the relevant formulas:

• To convert from Celsius to Fahrenheit, use (9/5 x C) + 32
• To convert from Fahrenheit to Celsius, use (F – 32) x 5/9
• To convert from Celsius to Kelvin, use C + 273.15
• To convert from Kelvin to Celsius, use K – 273.15
• To convert from Fahrenheit to Kelvin, use (F – 32) x 5/9 + 273.15
• To convert from Kelvin to Fahrenheit, use (K – 273.15) x 9/5 + 32

So, for example, if you wished to figure out what 20 °C was in Fahrenheit, the relevant calculation would be (20 x 9/5) + 32 = 68 °F.

However, you shouldn’t depend on manual methods alone, given the scope for human error to creep in – which in turn, can have severe implications in specialised and sensitive applications.

This is why it is important to use a reputable calculator to double-check the accuracy of your calculations. The electrical component supplier RS, for instance, offers an excellent online temperature unit converter for science and engineering purposes.

By developing an understanding of these respective temperature scales and the significant ways they vary, you can put yourself in a position to apply them in all manner of contexts with skill and confidence – thereby enhancing your work and day-to-day life.