BTU calculator
Enter the room’s length and width (or square footage) to get a cooling capacity in BTUs per hour from the ENERGY STAR room air conditioner chart. Optional shade, sun, occupancy and kitchen adjustments follow ENERGY STAR’s published guidance. Defaults are a 12 × 15 ft room.
How the calculator works
- Area: length × width, or enter square footage directly.
- Base BTU: look up the ENERGY STAR room air conditioner sizing table (cooling capacity for ~8 ft ceilings).
- Adjustments (ENERGY STAR): heavily shaded −10%; very sunny +10%; +600 BTU for each regular occupant beyond two; +4,000 BTU if used in a kitchen.
- Round down to the nearest thousand BTU/h.
ENERGY STAR cooling capacity chart
| Area (ft²) | Capacity (BTU/h) |
|---|---|
| 100 up to 150 | 5,000 |
| 150 up to 250 | 6,000 |
| 250 up to 300 | 7,000 |
| 300 up to 350 | 8,000 |
| 350 up to 400 | 9,000 |
| 400 up to 450 | 10,000 |
| 450 up to 550 | 12,000 |
| 550 up to 700 | 14,000 |
| 700 up to 1,000 | 18,000 |
| 1,000 up to 1,200 | 21,000 |
| 1,200 up to 1,400 | 23,000 |
| 1,400 up to 1,500 | 24,000 |
| 1,500 up to 2,000 | 30,000 |
| 2,000 up to 2,500 | 34,000 |
Cooling vs heating, and Manual J
This chart is for room cooling (window / room AC and as a starting point for a single-zone mini-split). It is not a whole-home heating load. For heating and for whole-house or multi-zone ductless systems, a licensed HVAC contractor should run an ACCA Manual J load calculation. Rules of thumb lose to a real load calc when insulation, windows, climate and orientation matter.
Related: mini split installation cost, heat pump installation cost, square footage calculator.
Oversizing cools the air before it removes humidity, leaving a clammy room (ENERGY STAR). Prefer the right size over “bigger is better.” For installs that handle refrigerant, hire an EPA Section 608–certified HVAC tech.
Sources
- ENERGY STAR, Room air conditioners: sizing chart (area → BTU/h; ~8 ft ceilings).
- ENERGY STAR, How to choose the right sized window AC: shade/sun ±10%, +600 BTU per extra person, +4,000 BTU kitchen, round down to nearest thousand.
- ACCA Manual J: residential load calculation (contractor practice for whole-home / multi-zone).