BTU Calculator

Calculate the BTU needed to heat or cool a room.

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BTU Calculator

Room Length (ft)

Room Width (ft)

Ceiling Height (ft)

Insulation Quality

What Is a BTU and How Is It Used?

BTU (British Thermal Unit) is a unit of heat energy — specifically, the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. BTU ratings are used to size air conditioners, heaters, and furnaces for rooms and buildings.

Common Uses

Sizing air conditioners for rooms (BTU per square foot)
Selecting the right furnace or boiler
Comparing heater outputs
Planning HVAC systems for commercial buildings

Frequently Asked Questions

How many BTUs do I need to cool a room?

A general rule: multiply room square footage by 20 for an estimate. A 200 sq ft room needs ~4,000 BTU; a 500 sq ft room needs ~10,000 BTU. Adjust upward for sunny rooms, high ceilings, or many occupants.

What is the difference between BTU and BTU/hr?

BTU measures total energy; BTU/hr (BTU per hour) measures power — the rate of energy delivery. Air conditioners and heaters are rated in BTU/hr. A 12,000 BTU/hr unit delivers 12,000 BTU of heating or cooling per hour.

Is this calculator free to use?

Yes. All calculators on zenicalculator.com are completely free with no registration required.

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