Free contractor tool
BTU Calculator for Room Air Conditioner Planning
Estimate room air conditioner cooling capacity from floor area in square feet. This uses the ENERGY STAR room-AC chart for an 8-foot ceiling, with its listed adjustments. It does not size a central system or heating equipment.
The starting inputs illustrate the method. Replace them with verified room measurements; no air conditioner is selected.
Your result
- Adjusted planning capacity (BTU/h)
- 6,000
- Area-chart capacity (BTU/h)
- 6,000
- Sun adjustment (BTU/h)
- 0
- Additional occupancy (BTU/h)
- 0
- Kitchen adjustment (BTU/h)
- 0
For room air conditioners and an 8-foot ceiling only. This is a planning estimate, not a central-system load calculation or equipment selection. Unusual spaces and other ceiling heights need a qualified assessment.
The calculation stays in your browser. No signup or email is needed.
Area band first, then explicit adjustments
The chart covers 100 to 2,500 sq ft. For a rectangular room, multiply length by width in feet; 12 feet 6 inches is 12.5 feet. Add separately measured areas for an irregular shape.
For an exact shared chart boundary, this tool uses the lower-capacity band: 250 sq ft gives 6,000 BTU/h, while an area above 250 through 300 gives 7,000. Heavily shaded rooms subtract 10% of the base; very sunny rooms add 10%. It then adds 600 BTU/h per regular occupant above two and 4,000 for a kitchen.
For example, 250 sq ft, very sunny, three people and a kitchen gives 6,000 + 600 + 600 + 4,000 = 11,200 BTU/h. That is a worksheet result, not a selected product.
A room-AC chart is not a building load calculation
The calculation does not assess climate, windows, insulation, air leakage, ducts, multiple connected rooms or the actual building load. It rejects areas outside the source chart instead of extrapolating.
For other ceiling heights, unusual conditions or central and ductless system selection, obtain an appropriate qualified assessment and follow the chosen product requirements. Do not use this result as a structural, electrical or installation check.