What Size Air Conditioner for Bedroom | Sizing That Actually Cools

Most bedrooms need a 5,000 to 8,000 BTU air conditioner, depending mainly on room square footage.

Getting the right air conditioner for your bedroom comes down to one measurement: the room’s square footage. Match that number to the right cooling capacity, and you’ll sleep comfortably without wasting electricity. Pick wrong, and you’ll deal with a room that never quite feels right—either too humid because the unit is oversized, or never cool enough because it’s undersized. Here’s how to get it right the first time.

The BTU Sizing Chart for Bedrooms

The quickest way to find your number is to measure the room and match it to the standard capacity chart. For a typical U.S. bedroom, the sweet spot usually lands between 5,000 and 8,000 BTU.

Start by measuring your bedroom’s length and width in feet, then multiply them together. That’s your square footage. If the cooling area isn’t a simple rectangle—say it has an alcove or a bump-out—ENERGY STAR recommends splitting the space into rectangles or triangles, calculating each section, and adding them together.

Once you have that number, match it to the capacity chart below. ENERGY STAR notes this chart assumes an 8-foot ceiling, so adjust accordingly if yours is taller.

Consumer Reports frames it a bit differently for bedrooms: for a small bedroom, home office, or guest room of 100 to 250 sq ft, look for a unit in the 5,000 to 6,500 BTU range. So a 120 sq ft bedroom at the low end might be fine with 5,000 BTU, while a 240 sq ft master bedroom will want closer to 6,500 or 7,000.

Room Factors That Change Your BTU Number

Square footage is the starting point, but your bedroom’s specific conditions can shift the number up or down. ENERGY STAR’s guidance accounts for these adjustments:

• Heavy shade: If your bedroom stays shaded most of the day, you can decrease capacity by about 10%.
• Very sunny exposure: South- or west-facing rooms with lots of direct sun should increase capacity by about 10%.
• More than two people: Each additional regular occupant adds roughly 600 BTU.
• Kitchen in the cooling area: Kitchens generate serious heat, so add about 4,000 BTU if the AC must cool one—though that rarely applies to a bedroom.

Here’s the catch worth remembering: these numbers apply to window and portable room air conditioners sized for U.S. rooms. If your bedroom connects to a hallway or another room without a door between them, Consumer Reports says to combine those spaces and size for the total area—the unit will struggle if it’s trying to cool space you didn’t measure.

Why Oversizing a Bedroom AC Backfires

It might feel logical to buy a bigger unit for faster cooling, but ENERGY STAR warns that an oversized air conditioner is less effective and can actually reduce comfort. That’s because a too-powerful unit cools the air quickly, then shuts off before it has run long enough to remove humidity from the room. The result is a bedroom that feels cold but clammy—and a unit that cycles on and off constantly, wasting energy.

If a 6,000 BTU unit fits your 200 sq ft bedroom, don’t step up to 8,000 BTU “just to be safe.” The undersized unit has the opposite problem: it runs constantly, struggles to reach your set temperature on the hottest days, and wears itself out faster. The right size is the one that matches your measured space plus the condition adjustments above.

Energy Efficiency and Buying the Right Unit

When you’ve settled on the right BTU size, the next question is efficiency. Consumer Reports recommends looking for an ENERGY STAR label and, for window units, an EER (energy efficiency ratio) of 10 or above. A higher EER means the unit delivers more cooling per watt of electricity—something you’ll notice on your summer utility bill since a bedroom AC runs nightly.

Once you know your square footage and BTU target, browsing our roundup of top bedroom air conditioners gives you tested models that match each size class. You can filter by your room’s needs and compare efficiency ratings side by side.