Thermal efficiency

Thermal efficiency is a measure of how much energy we get out of something compared to how much energy we put in. It measures how efficiently a machine or engine works when it turns energy into useful work. For example, if we put 10 units of energy into a machine, and it only gives us 5 units of useful work out, then the thermal efficiency of the machine is 5/10, or 50%. That means it only used half of the energy it was given. If a machine gives us all the energy it was given back as useful work, then its thermal efficiency is 100%.