The British Thermal Unit (BTU) is the unit for measuring the heating capacity of a heater. A BTU is the amount of heat needed to raise 1 pound of water temperature by 1 degree Fahrenheit. You can determine the number of BTUs needed to heat your space with just a few calculations. The BTUs needed to heat a room are determined by its volume, level of insulation and climate.

Calculate the volume of your room to determine the number of BTUs.

Step 1

Measure the length, width and height of the room in feet.

Step 2

Multiply the length times the width times the height to calculate the volume in cubic feet.

Step 3

Multiply the room's cubic footage by 4 if its walls contain fewer than 3 inches of insulation. Multiply it by 3 if the insulation is at least 3 1/2 inches thick and by 2 if the insulation is 6 inches thick or more.

Step 4

Double the figure you arrived at in Step 3 if you live in a cold climate or prefer indoor winter temperatures well above room temperature.

Step 5

Convert watts to BTUs. Many space heaters list their capacity in watts. To translate watts to BTUs, multiply the listed watts by 3.4.