Calculator
BTU Calculator
Size a window unit or mini split for a single room.
Model reviewed August 2026
BTU needed
6,000 BTU/hr
- Mini split size
- 0.5 tons
- Typical unit costInstalled mini split
- $600 – $1,300
Estimates only. Local pricing, site conditions and code requirements change the real number.
The formula
BTU = room area x 20, +10% for sunny rooms, +600 per extra occupant, +4,000 for kitchens
The 20 BTU per square foot baseline comes from ENERGY STAR room air conditioner guidance.
Worked example
A sunny 300 sq ft bedroom with two people needs about 7,200 BTU — a 7,000 to 8,000 BTU unit.
Frequently asked questions
How many BTU per square foot?
About 20 BTU per square foot for a room unit in a typical climate. Hot, humid and sun-exposed rooms push that toward 25.
Sources
Sources & verification
- ENERGY STAR sizing and efficiency guidance
- ACCA Manual J / Manual S sizing standards
- AHRI equipment performance directory
- International Code Council (IRC/IBC)
Model vintage August 2026. The links above are the issuing agencies' own pages — we publish them so you can confirm the current rule yourself, not as evidence that each fact on this page was re-checked with them today. Cost figures are modeled estimates based on national baselines adjusted for local labor and material pricing, not quotes. Permit rules change; confirm with the building department before starting work.