đĨ BTU Calculator
Calculate the BTU heating and cooling capacity needed for any room based on dimensions, insulation, windows, and climate zone.
How to Use This Calculator
Enter your room dimensions (length, width, and ceiling height) to calculate the square footage. Then select your insulation quality â if you're unsure, "Average" is a safe choice for most homes built after 1980. Add the number of windows in the room and select your sun exposure level. Include the number of people who regularly use the room. Finally, select your climate zone based on your geographic location. Results update instantly as you adjust any input.
Understanding Your Results
The BTU (British Thermal Unit) results show how much heating and cooling capacity your room needs. Cooling BTU is typically lower than heating BTU. The tonnage recommendation converts cooling BTU into standard AC unit sizes (1 ton = 12,000 BTU). Use these numbers when shopping for window units, mini splits, or discussing options with your HVAC contractor.
Frequently Asked Questions
What is a BTU?
A BTU (British Thermal Unit) is a unit of heat energy. One BTU is the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. In HVAC, BTUs measure heating and cooling capacity.
How many BTU do I need per square foot?
A general rule of thumb is 20 BTU per square foot for cooling. However, this varies based on insulation quality, ceiling height, climate zone, sun exposure, and number of occupants. Our calculator accounts for all these factors.
What size AC unit do I need based on BTU?
AC units are measured in tons, where 1 ton equals 12,000 BTU. A 24,000 BTU requirement would need a 2-ton unit. Our calculator automatically converts BTU to tonnage for you.
Do I need more BTU for heating or cooling?
Heating typically requires more BTU than cooling for the same space, especially in cold climates. Our calculator provides separate heating and cooling BTU recommendations.