❄️ BTU Calculator (Air Conditioner Sizing)
Enter the room area and a few conditions to estimate the air-conditioner cooling capacity you need, in BTU per hour.
Recommended cooling capacity
6,000 BTU/h
≈ 0.50 tons · 1758 watts
Sizing follows the ENERGY STAR guideline of about 20 BTU per square foot, adjusted for a very sunny (+10%) or heavily shaded (−10%) room, extra occupants (+600 BTU each beyond two) and kitchens (+4,000 BTU for appliance heat). Oversizing an AC makes it short-cycle and dehumidify poorly, so bigger isn\'t better. For whole-home or high-ceiling spaces, a Manual J load calculation is more precise. 🔒 In your browser.
How the btu calculator (air conditioner sizing) works
A common sizing guideline (from ENERGY STAR) is about 20 BTU per hour per square foot of floor area. The tool starts there and adjusts: +10% for a very sunny room or −10% for a heavily shaded one, +600 BTU for each regular occupant beyond two, and +4,000 BTU if it's a kitchen (to cover appliance heat). The result is the recommended cooling capacity in BTU/h, also shown in tons and watts.
Bigger is not better: an oversized air conditioner cools the air quickly but short-cycles, so it removes less humidity and wastes energy, leaving the room cold and clammy. This is a quick estimate for a single room; for a whole house, high ceilings or ducted systems, a proper Manual J heat-load calculation accounts for insulation, windows and climate.
Frequently asked questions
How many BTU do I need to cool a room?
Roughly 20 BTU per hour per square foot, so about 6,000 BTU for a 300 ft² room — then adjust up for sun, extra people or a kitchen. This tool applies those adjustments for you.
How do you calculate air conditioner size?
Multiply the room's area by ~20 BTU/ft², then add for heat gains: +10% if very sunny, +600 BTU per person beyond two, +4,000 for a kitchen. The result is the cooling capacity in BTU/h (12,000 BTU = 1 ton).
What size AC for a 300 square foot room?
About 6,000 BTU/h as a baseline (300 × 20). A sunny 300 ft² room, or one with several people, would want a bit more — the tool shows the adjusted figure.
Is a bigger BTU air conditioner better?
No. An oversized unit cools too fast and shuts off before removing humidity, so the room feels cold and damp and the compressor wears from short-cycling. Match the capacity to the room.
How many BTU is a ton of cooling?
12,000 BTU per hour equals one ton of cooling. So a 24,000 BTU/h system is a 2-ton unit. The tool shows tons alongside BTU.