# Question #f8bfc

A British thermal unit, or Btu, is defined as the amount of heat needed to raise the temperature of $\text{1 lb}$ of water by ${1}^{\circ} \text{F}$.
This means that if you have a $\text{1-lb}$ sample of water at a temperature of, say, ${77}^{\circ} \text{F}$, you would need to supply it with $\text{1 Btu}$ of heat in order to get its temperature to increase to ${78}^{\circ} \text{F}$.