Apartments break the one-room, one-unit pattern, so it helps to think in zones. A studio is one zone: the whole apartment is a single open space with the kitchen in it, so size the full floor area with the kitchen adder, and the table below does exactly that. A one- or two-bedroom apartment is at least two zones, one for the living/kitchen area and one per bedroom, and a single big window unit in the living room almost never cools the bedrooms through a doorway.
Apartments have a few features that shift the load compared with a house. Middle-floor units with neighbors above and below have only one or two exterior walls, which behaves like 'good insulation' even in older buildings. Top-floor units under a flat roof are the opposite and often run 10 to 20% hotter than the same footprint below. Corner units with windows on two sides earn the sunny adjustment. Ask which you have before trusting the average row.
For the living zone of a 700 sq ft one-bedroom, expect 10,000 to 12,000 BTU including the kitchen; the bedroom on its own wants 5,000 to 6,000 BTU. Two right-sized units cost about the same as one oversized 18,000 BTU unit and are dramatically more comfortable, because each room reaches its own temperature and the bedroom unit can run quietly on low overnight.
Cooling BTU by apartment size
Baseline: average sun, average insulation, moderate climate, 8 ft ceiling, 2 people, kitchen included.
| Floor area | Best case | Baseline | Worst case | Unit to buy |
|---|---|---|---|---|
| 400 sq ft | 10,500 | 12,000 | 14,100 | 12,000 BTU |
| 500 sq ft | 12,100 | 14,000 | 16,700 | 14,000 BTU |
| 600 sq ft | 13,700 | 16,000 | 19,200 | 18,000 BTU |
| 700 sq ft | 15,300 | 18,000 | 21,700 | 18,000 BTU |
| 800 sq ft | 17,000 | 20,000 | 24,200 | 24,000 BTU |
| 1,000 sq ft | 20,200 | 24,000 | 29,300 | 24,000 BTU |
Best case = good insulation and heavy shade; worst case = poor insulation and full sun.
Apartment-specific advice
Studios: one unit, whole area, kitchen ticked
Measure the whole floor including the kitchen nook and bathroom if its door stays open. Tick the kitchen box. Most 400–550 sq ft studios land at 10,000–12,000 BTU.
One-bedrooms: two units beat one
Size the living/kitchen zone and the bedroom separately. A 10,000 BTU living room unit plus a 5,000 BTU bedroom unit outperforms a single 15,000 BTU unit every time.
Check the window and the wiring
Many apartment windows cannot take a unit over 12,000 BTU physically, and most bedroom outlets are 15 A circuits that top out around 12,000 BTU. Above that you need a dedicated 20 A or 240 V circuit, which usually means landlord permission.
Common questions
What size AC do I need for a 600 sq ft apartment?
As a single open zone with a kitchen, about 16,000 BTU, so a 14,000–18,000 BTU unit. Split into a 450 sq ft living/kitchen zone and a 150 sq ft bedroom, you would want about 13,000 BTU for the living area and 5,000 BTU for the bedroom.
Is a portable AC good for an apartment?
Portables are the go-to where window units are banned or the windows are casement style. Compare using the SACC rating, and expect a 10,000 BTU (ASHRAE) portable to deliver roughly 6,500 BTU of real cooling.
Does floor level matter for AC size?
Yes. Top-floor units under the roof can need 10–20% more cooling than the same layout on a middle floor. Ground-floor units are often the coolest. Use 'poor insulation' for a top-floor unit in an older building.