Room volume: — cu ft | Recommended equipment: —
Result Summary
| BTU/hr | — |
| Tons / Watts | — |
| Recommended equipment | — |
| Room volume | — |
| Operating cost | — |
BTU by Room Size (cooling baseline)
| Room area | Approx. cooling BTU/hr |
|---|---|
| 150 – 250 sq ft | 5,000 – 6,000 |
| 250 – 350 sq ft | 7,000 – 8,000 |
| 350 – 450 sq ft | 10,000 |
| 450 – 550 sq ft | 12,000 |
| 550 – 700 sq ft | 14,000 |
| 700 – 1,000 sq ft | 18,000 |
Climate Adjustment
| Climate | Cooling factor | Heating BTU/sq ft |
|---|---|---|
| Cold | 0.85x | ~50 – 60 |
| Cool | 0.92x | ~45 |
| Moderate | 1.00x | ~40 |
| Warm | 1.15x | ~30 |
| Hot | 1.30x | ~25 |
What Size BTU Do I Need?
A BTU, or British Thermal Unit, is the amount of heat needed to raise one pound of water by one degree Fahrenheit. For heating and cooling, equipment is rated in BTU per hour: how much heat it can add or remove each hour. To size a room, start from its area and a baseline BTU per square foot, then adjust for ceiling height, climate, insulation, sun, windows, occupants, and appliances. The calculator above does this for both heating and cooling, and converts the result to tons and watts so you can match it to any equipment rating.
BTU vs Tons vs Watts
These three units all describe the same thing, the rate of heat moved, in different scales. One ton of cooling equals 12,000 BTU per hour, a term left over from comparing air conditioning to melting ice. One watt equals about 3.412 BTU per hour, so to convert BTU per hour to watts you multiply by 0.293. Window air conditioners and furnaces are usually rated in BTU, central air conditioners in tons, and electric heaters in watts, so being able to convert lets you compare any two units on equal footing.
Frequently Asked Questions
How many BTU per square foot? Cooling needs roughly 20 BTU per square foot as a baseline; heating ranges from about 25 in hot climates to 60 in cold ones.
Why are heating and cooling BTU different? Heating fights the outdoor cold, which is harsher in winter than summer heat in most climates, so heating loads are often larger in cold zones.
How do I convert BTU to tons? Divide BTU per hour by 12,000. An 18,000 BTU unit is 1.5 tons.
Is bigger equipment better? No. Oversized equipment short-cycles, wastes energy, and controls humidity poorly. Match the load instead.