❄️ BTU Calculator
An undersized AC runs forever without cooling; an oversized one short-cycles and leaves humidity behind. The industry rule of thumb — 20 BTU per square foot — gets you in the right range for a standard room.
The calculator also converts to tons (12,000 BTU = 1 ton), the unit central systems are sold in.
How to use this calculator
Enter the room's floor area in square feet and the calculator returns the cooling power needed in BTU and in tons.
- Measure the room's length and width in feet and multiply them for the area.
- Enter the Room area in square feet.
- Read the BTU figure, the hero result.
- Check the tonnage if you are shopping for a central system.
Frequently asked questions
What does the BTU Calculator compute?
It multiplies your room area by 20 BTU per square foot, the industry rule of thumb for standard rooms, and converts the result to tons by dividing by 12,000.
Can you give a worked example?
A 500 square foot room needs 10,000 BTU, which is 0.83 tons of cooling.
What is a ton of cooling?
One ton equals 12,000 BTU per hour, a historical term from the cooling power of a ton of ice. Central air systems are sized in tons.
When does the 20 BTU rule not apply?
It assumes standard 8 foot ceilings and normal sun exposure. Add about 10 percent for very sunny rooms or kitchens, and get a professional load calculation for whole-house systems.