What Size Air Conditioner Do You Need?
Most bedrooms (150 to 250 sq ft) need a 6,000 BTU air conditioner. Enter your room below: the calculator uses ENERGY STAR's sizing chart and shows the most efficient unit to buy at your size.1
01 / BTU chart
BTU chart by room size
ENERGY STAR's chart for an 8-foot ceiling. Window ACs come in fewer sizes than the chart lists, so "Buy" is the smallest common size that covers it.1
| Room (sq ft) | BTU needed | Buy (BTU) |
|---|---|---|
| 100–150 | 5,000 | 5,000 |
| 150–250 | 6,000 | 6,000 |
| 250–300 | 7,000 | 8,000 |
| 300–350 | 8,000 | 8,000 |
| 350–400 | 9,000 | 10,000 |
| 400–450 | 10,000 | 10,000 |
| 450–550 | 12,000 | 12,000 |
| 550–700 | 14,000 | 14,000 |
| 700–1,000 | 18,000 | 18,000 |
| 1,000–1,200 | 21,000 | 24,000 |
| 1,200–1,400 | 23,000 | 24,000 |
| 1,400–1,500 | 24,000 | 24,000 |
| 1,500–2,000 | 30,000 | Mini split |
| 2,000–2,500 | 34,000 | Mini split |
Rows from ENERGY STAR, read October 12, 2026. Over 1,500 sq ft, one window AC can't cool the space well: see window AC or mini split?
02 / What to buy
The most efficient window AC at each size
At each size, the window AC with the highest certified efficiency (CEER) that we found for sale on Amazon. Higher CEER means less electricity for the same cooling.2
| Size | Unit | CEER | A year to run | Price | Buy |
|---|---|---|---|---|---|
| 5,000 BTU100 to 150 sq ft | No certified 5,000 BTU window AC with a live Amazon listing today. The 6,000 BTU pick below is the smallest. | ||||
| 6,000 BTU150 to 250 sq ft | Midea MAW06V1UBLall 2 at this size | 15.1 | $56 | $314.99Oct 17 | Check price |
| 8,000 BTU250 to 350 sq ft | Midea MAW08V1KWT-Aall 14 at this size | 15.1 | $73 | $259.99Oct 17 | Check price |
| 10,000 BTU350 to 450 sq ft | TCL T10WV9Sall 10 at this size | 16 | $88 | $439.99Oct 17 | Check price |
| 12,000 BTU450 to 550 sq ft | TCL T12WV9Sall 6 at this size | 16 | $106 | $489.99Oct 17 | Check price |
| 14,000 BTU550 to 700 sq ft | TCL T14WV9Sall 7 at this size | 16 | $124 | $629.99Oct 17 | Check price |
| 18,000 BTU700 to 1,000 sq ft | Keystone KSTAW182WAall 2 at this size | 15 | $169 | $656.99Oct 17 | Check price |
| 24,000 BTU1,000 to 1,500 sq ft | Perfect Aire 1PACV25000Eall 1 at this size | 13.3 | $255 | $963.75Oct 17 | Check price |
Only units whose own Amazon listing we found buyable; ties go to the lower price. Prices are from the date shown. Yearly running cost is computed by us from the certified rating and the U.S. average electricity price (see the methodology).
03 / Your room
Five things that change the number
| If your room is | Change | Example: 300 sq ft (8,000 BTU) |
|---|---|---|
| Heavily shaded | Reduce by 10%Source: ENERGY STAR | 7,200 BTU → buy 8,000 |
| Very sunny | Increase by 10%Source: ENERGY STAR | 8,800 BTU → buy 10,000 |
| Used by more than 2 people | Add 600 BTU per extra personSource: ENERGY STAR | 4 people: 9,200 BTU → buy 10,000 |
| A kitchen | Add 4,000 BTUSource: ENERGY STAR | 12,000 BTU → buy 12,000 |
| Ceiling over 8 ft | Scale by height ÷ 8 (room volume)Source: computed by us | 10 ft: 10,000 BTU → buy 10,000 |
ENERGY STAR gives the first four rules.1 It says its chart assumes an 8-foot ceiling but gives no number for taller ones, so the height step is our own estimate. When several apply, the calculator applies sun or shade and ceiling height to the chart number, then adds people and kitchen.
04 / Size up or down?
Why bigger is not better
- A unit that is too big leaves the room damp. ENERGY STAR says an oversized unit cools the room before it has a chance to remove the humidity, so cool, moist air makes the room feel clammy.1
- It also costs more to buy and run. ENERGY STAR: an oversized air conditioner costs more to purchase, wastes energy and does not provide better cooling.1
- So buy the smallest size that covers your number. If your number lands between sizes, go up one size, not two.
05 / Questions
Frequently asked
- How many BTU do I need for a 12 x 12 room?
- A 12 x 12 room is 144 sq ft, so ENERGY STAR's chart says 5,000 BTU (100 to 150 sq ft). Add 10% if the room is very sunny. We don't list a certified 5,000 BTU window unit with a live Amazon listing today; the smallest is 6,000 BTU. 13
- What size air conditioner do I need for 500 sq ft?
- 12,000 BTU. ENERGY STAR's chart puts 450 to 550 sq ft at 12,000 BTU. Go to 14,000 BTU for a very sunny room or one used by more than two people every day, and to 18,000 BTU for a kitchen. 1
- Is a bigger air conditioner better?
- No. ENERGY STAR says an oversized unit costs more, wastes energy and does not cool better. If it is too large, it cools the room before it removes the humidity, so the room feels damp and clammy. Buy the smallest size that covers your number. 1
- Do high ceilings change the BTU I need?
- Yes. ENERGY STAR's chart assumes an 8-foot ceiling but gives no number for taller ones. The calculator scales the chart by room volume, so a 10-foot ceiling adds 25%. That step is our own math, not an ENERGY STAR figure. 1
- How do I measure my room?
- Multiply length by width in feet. For an L-shaped room, split it into two rectangles and add them. ENERGY STAR says to measure in feet and turn inches into fractions of a foot (6 inches = 0.5 ft). 1
06 / Sources
Where these numbers come from
- 1
- 2
- 3
Related: best window air conditioners · for small rooms · for large rooms · what size mini split for 500 sq ft · window AC or mini split?