Whilst heat can be used to calculate how much internal energy a substance contains, temperature represents the intensity of that energy.


Temperature is a measure of the average kinetic energy that the molecules of a substance contain. Substances with more kinetic energy have a higher temperature than substances with lower kinetic energy.


In order to compare the temperature of substances, a common measurement scale is required. Common units of measurement for temperature are Celsius (°C), Fahrenheit (°F) and Kelvin (K).

  • Celsius – tends to be favoured in Europe. Fresh water boils at 100°C and freezes at 0°C.
  • Fahrenheit – tends to be favoured in the Americas. Fresh water boils at 212 °F and freezes at 32°F. Saltwater freezes at 0 °F. Fahrenheit is an imperial form of measurement.
  • Kelvin – one of the seven SI units (International System of Units). Fresh water boils at 373 K and freezes at 273 K. One Kelvin is equal in magnitude to one Celsius, but the scales used are different. Kelvin is a metric form of measurement.

Celsius and Fahrenheit Thermometer Comparison

Celsius and Fahrenheit Thermometer Comparison

Temperature Conversions

Celsius to Fahrenheit

(°C × 9/5) + 32 = °F


(1°C × 9/5) + 32 = 33.8°F

Fahrenheit to Celsius

(°F − 32) × 5/9 = °C


(1°F − 32) × 5/9 = -17.22°C


Additional Resources