From square feet to tons in two steps
Estimate the cooling load at about 20 BTU per square foot, then divide by 12,000 to get tons, since 1 ton of cooling is 12,000 BTU/h. A 600 sq ft room is roughly 12,000 BTU, or 1 ton. This is a starting point; climate, sun exposure and insulation move it up or down.
Quick reference by home size
| Area | Approx. BTU/h | Tons |
|---|---|---|
| 500 sq ft | 10,000 | ~1 |
| 1,000 sq ft | 20,000 | ~1.5–2 |
| 1,500 sq ft | 30,000 | ~2.5–3 |
| 2,000 sq ft | 40,000 | ~3–3.5 |
| 2,500 sq ft | 50,000 | ~4–4.5 |
| 3,000 sq ft | 60,000 | ~5 |
Units are sold in half-ton steps (1, 1.5, 2, 2.5, 3, 3.5, 4, 5 tons). When in doubt, round down rather than up.
What pushes the number up or down
- Climate. A hot, humid region (Miami, the Gulf Coast) needs roughly 30% more than a temperate one; a cool northern climate needs less.
- Sun and orientation. West- and south-facing rooms take the most afternoon heat and add about 10–15%.
- Insulation and windows. Poor insulation or single-pane glass adds around 25%; excellent insulation cuts it by up to 30%.
- Heat sources. Add roughly 4,000 BTU for a kitchen, and about 600 BTU per person for rooms that are regularly crowded.
Common questions
How many tons of AC do I need per square foot?
A rough rule is 20 BTU per square foot for a room, and 1 ton of cooling per 400 to 600 square feet of home. So a 1500 sq ft house lands around 2.5 to 3.5 tons before adjusting for climate, sun and insulation.
What does a ton of air conditioning mean?
One ton equals 12,000 BTU per hour. The name comes from the cooling a ton of ice gives as it melts over a day. So a 3-ton unit is 36,000 BTU/h; it has nothing to do with the units weight.
Is a bigger AC unit better?
No. An oversized unit cools the air fast then shuts off before it pulls out the humidity, leaving the room cold and clammy. The short on-off cycles also wear the compressor and raise running costs. Size to the load, not above it.
