A typical American bedroom runs 120 to 200 square feet, which lands squarely in 5,000 to 6,000 BTU territory using the standard 20 BTU per square foot rule. That is the smallest class of window air conditioner sold, and it is genuinely enough. The most common bedroom sizing mistake is not going too small; it is buying a 10,000 or 12,000 BTU unit because it was on sale and then wondering why the room feels cold and damp at 3 a.m.
Bedrooms have two things going for them. The load is low because there are usually only two people in the room, both asleep and producing little heat, with no cooking and few electronics running. And the room is mostly used at night, when the sun is not beating on the windows, so the daytime peak that a living room has to fight simply does not happen. A bedroom that gets brutal afternoon sun still deserves the +10% sunny adjustment, because the walls and furniture soak up that heat and release it into the evening.
The one adjustment that pushes bedrooms up a size is a large primary suite with a walk-in closet and an attached bathroom the door stays open to. Add that square footage to the room area, since the air conditioner has to cool it too. For rooms over 250 square feet see the master bedroom page.
Cooling BTU by bedroom size
Baseline: average sun, average insulation, moderate climate, 8 ft ceiling, 2 people.
| Floor area | Best case | Baseline | Worst case | Unit to buy |
|---|---|---|---|---|
| 100 sq ft | 1,600 | 2,000 | 2,500 | 5,000 BTU |
| 120 sq ft | 1,900 | 2,400 | 3,000 | 5,000 BTU |
| 150 sq ft | 2,400 | 3,000 | 3,800 | 5,000 BTU |
| 180 sq ft | 2,900 | 3,600 | 4,600 | 5,000 BTU |
| 200 sq ft | 3,200 | 4,000 | 5,100 | 5,000 BTU |
| 250 sq ft | 4,100 | 5,000 | 6,300 | 5,000 BTU |
Best case = good insulation and heavy shade; worst case = poor insulation and full sun.
Bedroom-specific advice
Prioritize noise rating over BTU once the size is right
Window units for bedrooms are sold at 5,000 to 8,000 BTU with noise ratings anywhere from 42 to 60 dB. A 6,000 BTU unit at 45 dB will sleep far better than an 8,000 BTU unit at 58 dB. Inverter (variable-speed) models run quietest because they idle at low speed instead of cycling on and off.
A ceiling fan lets you set the AC a couple of degrees warmer
Moving air feels about 3 to 4°F cooler on skin. Running a fan with the AC set at 76°F usually feels the same as 73°F without one, and cuts compressor runtime noticeably.
Closed door versus open door
If you sleep with the door open, warm air from the hallway drifts in all night. Either size for the room only and close the door, or add roughly half the hallway area to your square footage.
Common questions
Is 5,000 BTU enough for a bedroom?
Yes for bedrooms up to about 150 square feet with average sun and insulation, and up to about 250 square feet if the room is shaded and well insulated. A 12 by 12 bedroom (144 sq ft) at 20 BTU per square foot needs about 2,900 BTU, so a 5,000 BTU unit has comfortable headroom.
Is 8,000 BTU too much for a small bedroom?
For a 120 to 150 sq ft bedroom, 8,000 BTU is roughly double the calculated load. The unit will cool the air fast, shut off before it removes much humidity, and the room will feel clammy. It also cycles more, which is louder and harder on the compressor. Stick with 5,000 or 6,000 BTU.
What about a portable AC for a bedroom?
Portable units are rated two ways. The old ASHRAE number (say, 8,000 BTU) overstates real cooling; the newer DOE SACC rating is what you actually get, often 5,000 to 5,500 BTU for an '8,000 BTU' portable. Use the SACC number when comparing against your calculated load.