The single biggest mistake people make buying an AC is going too big.
A 14,000 BTU unit in a 200-square-foot bedroom will cool the room in five minutes flat — and then it'll shut off, leaving the air clammy and the room damp. AC isn't just about cooling; it's about pulling humidity out. An oversized unit doesn't run long enough to do that. The room ends up cold and muggy.
Going too small is the other failure mode: the unit runs constantly, never quite catches up, and burns out three summers early.
The rule of thumb
Use roughly 20 BTU per square foot as your baseline. Then adjust up or down.
| Room size (sq ft) | BTU range | Typical use |
|---|---|---|
| 100–150 | 5,000 | Small bedroom, small office |
| 150–250 | 6,000–7,000 | Bedroom |
| 250–350 | 8,000–9,000 | Bedroom or living room |
| 350–450 | 10,000–12,000 | Living room |
| 450–550 | 12,000–14,000 | Large living room |
| 550–700 | 14,000–18,000 | Open-plan studio |
| 700–1,000 | 18,000–24,000 | Large open plan |
Adjustments that matter
- Sunny room? Bump up one tier. South- and west-facing windows can add 10–15% to the heat load.
- Kitchen? Bump up one tier. The stove and oven are a heat source you're trying to neutralize.
- High ceilings (9 ft+)? Bump up one tier. You're cooling more air than the floor area suggests.
- Shaded north-facing room? You can usually go down one tier.
- A lot of people in the room often? Bump up. Each person adds roughly 600 BTU of heat.
Why this matters more than the price tag
A right-sized AC will:
- Cool the room evenly without hot spots.
- Run long enough to dehumidify, so the air feels crisp instead of cold-and-clammy.
- Cycle on and off less, which means lower bills and a longer life.
A right-sized AC at a slightly higher price usually pays for itself in two or three summers in lower electric bills alone.
What we do
When you check out, you tell us the room and we'll flag it if your size looks off. If you'd rather just call (800) 555-1212 before you order, we'll size it for you — that's free, and it's faster than you re-reading this guide.
Need help picking? Browse all our air conditioners — every product page shows the room-size range the unit is rated for.