Home & Cooling
Find the right air conditioner capacity for your room. Input room dimensions, ceiling height, sun exposure, and occupants to get your recommended BTU.
Recommended BTU
4,500 BTU/h
This is a guide. For precise sizing, consult an HVAC professional. High occupancy, kitchens, or significant heat sources may require larger units.
BTU stands for British Thermal Unit, a measure of cooling capacity. One BTU is the energy needed to cool one pound of water by one degree Fahrenheit. Air conditioning units are rated in BTU/h (BTUs per hour). A room's cooling needs depend on size, insulation, windows, occupancy, and heat sources. The right BTU rating ensures comfort without wasting energy.
Enter your room's length and width in feet to calculate its area. Select ceiling height (standard or high). Choose sun exposure (shaded, normal, or sunny). Enter the number of occupants. The calculator applies a base formula (20 BTU per square foot), then adjusts for ceiling height, sunlight, and occupancy. The result shows recommended BTU and tonnage.
Base BTU = Room Area (sq ft) × 20. Then adjust: +10% for high ceilings, ±10% for sunny/shaded, +600 BTU per extra occupant over 2.The baseline is 20 BTU per square foot of room area. A 15×15 ft room (225 sq ft) needs 225 × 20 = 4500 BTU base. Sunny rooms need extra cooling (+10%), shaded rooms need less (-10%). High ceilings hold more volume so require more cooling (+10%). Each occupant beyond 2 adds body heat: +600 BTU per person. The final number is your recommended capacity.
| Input | Result | Notes |
|---|---|---|
| Room 15×15 ft, standard height, normal sun, 2 occupants | 4,500 BTU | Base = 225 sq ft × 20 = 4,500 BTU; no adjustments needed; ≈ 0.4 tons |
| Room 20×20 ft, high ceiling, sunny, 4 occupants | 10,880 BTU | Base = 400 × 20 = 8,000; +10% ceiling = +800; +10% sunny = +800; 2 extra occupants = +1,200; Total = 10,800 ≈ 0.9 tons |
| Room 12×14 ft, standard height, shaded, 2 occupants | 3,024 BTU | Base = 168 × 20 = 3,360; -10% shaded = -336; Total = 3,024 ≈ 0.25 tons |
One ton of air conditioning = 12,000 BTU/h. A 2-ton unit = 24,000 BTU, 3-ton = 36,000 BTU, etc. The term comes from ice tonnage in older refrigeration.
Higher ceilings mean more air volume to cool. The calculator adds 10% for high ceilings (≥10 ft) because the same cooling must cover extra space.
Direct sunlight can add 20–30% to cooling load. The calculator uses ±10% as a conservative adjustment. South- and west-facing windows are hottest.
Yes. Stoves, ovens, and refrigerators generate heat. Kitchens may need +4,000–6,000 extra BTU. This tool does not include kitchens automatically; adjust manually if needed.
This tool is for single rooms. For central AC, calculate each room, add them up, or hire an HVAC contractor for a manual J load calculation.
Divide odd shapes into rectangles, calculate each area, and add them. Or estimate an average length and width. The calculator works with the total area.