BTU Calculator

BTU Calculator

AC BTU Calculator

Use this calculator to estimate the cooling needs of a typical room or house, such as finding out the power of a window air conditioner needed for an apartment room or the central air conditioner for an entire house.

Room Ceiling Height
Number of People
Inside Regularly
Insulation Condition
Sun Exposure

General Purpose AC or Heating BTU Calculator

This is a general purpose calculator that helps estimate the BTUs required to heat or cool an area. The desired temperature change is the necessary increase/decrease from outdoor temperature to reach the desired indoor temperature. As an example, an unheated Boston home during winter could reach temperatures as low as -5°F. To reach a temperature of 75°F, it requires a desired temperature increase of 80°F. This calculator can only gauge rough estimates.

Room/House Width
Room/House Length
Ceiling Height
Insulation Condition
Desired Temperature
Increase or Decrease
e.g. 75°F for Boston winter, 45°F for Atlanta winter.

What is a BTU?

The British Thermal Unit, or BTU, is an energy unit. It is approximately the energy needed to heat one pound of water by 1 degree Fahrenheit. 1 BTU = 1,055 joules, 252 calories, 0.293 watt-hours, or the energy released by burning one match. 1 watt is approximately 3.412 BTU per hour.

BTU is often used as a point of reference for comparing different fuels. Even though they're physical commodities and are quantified accordingly, such as by volume or barrels, they can be converted to BTUs depending on the energy or heat content inherent in each quantity. BTU as a unit of measurement is more useful than physical quantity because of fuel's intrinsic value as an energy source. This allows many different commodities with intrinsic energy properties, such as natural gas and oil, to be compared and contrasted.

BTU can also be used pragmatically as a point of reference for the amount of heat that an appliance generates; the higher the BTU rating of an appliance, the greater the heating capacity. As for air conditioning in homes, even though ACs are meant to cool homes, BTUs on the technical label refer to how much heat the air conditioner can remove from their respective surrounding air.

Size and Ceiling Height

Unsurprisingly, a smaller room requires fewer BTUs to cool/heat. Typically, BTU usage is measured based on the volume of the space.

The following is a rough estimation of the cooling capacity a cooling system would need to effectively cool a room/house based only on the square footage of the room/house, as provided by

Area To Be Cooled (square feet)Capacity Needed (BTUs per hour)
100 to 1505,000
150 to 2506,000
250 to 3007,000
300 to 3508,000
350 to 4009,000
400 to 45010,000
450 to 55012,000
550 to 70014,000
700 to 1,00018,000
1,000 to 1,20021,000
1,200 to 1,40023,000
1,400 to 1,50024,000
1,500 to 2,00030,000
2,000 to 2,50034,000
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