What Size Air Conditioner Do I Need for a 150 Sq Ft Room?
150 sq ft is the shared edge of the 5,000 and 6,000 BTU/hr rows, so the row choice comes before the 10% tweaks.
Full breakdown: BTU per square foot.
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Capacity from the chart
| Area to be cooled | Capacity needed | Source |
|---|---|---|
| 100 up to 150 sq ft | 5,000 BTU/hr | ENERGY STAR |
| 150 up to 250 sq ft | 6,000 BTU/hr | ENERGY STAR |
Treat 150 sq ft as a tape-measure problem, not a guess. ENERGY STAR says to multiply length by width. Leftover inches convert as 3 in = .25 ft, 6 in = .5 ft, and 9 in = .75 ft. If the product of those measurements is still on the 100 up to 150 side, the row is 5,000 BTU/hr. If the inches push the area onto 150 up to 250, the row is 6,000 BTU/hr before any sun or shade tweak.
How to size it
Pick the row, then apply a single adjustment. Shade and sun are opposites: do not take 10% off and add 10% in the same pass. The chart does not tell you to average 5,000 and 6,000.
| Adjustment | On the 5,000 row | On the 6,000 row | Source |
|---|---|---|---|
| Heavily shaded, reduce capacity 10% | 5,000 − 10% = 4,500 BTU/hr | 6,000 − 10% = 5,400 BTU/hr | ENERGY STAR |
| Very sunny, increase capacity 10% | 5,000 + 10% = 5,500 BTU/hr | 6,000 + 10% = 6,600 BTU/hr | ENERGY STAR |
| Each additional person beyond two | 5,000 + 600 BTU/hr = 5,600 BTU/hr | 6,000 + 600 BTU/hr = 6,600 BTU/hr | ENERGY STAR |
| Unit used in a kitchen | 5,000 + 4,000 BTU/hr = 9,000 BTU/hr | 6,000 + 4,000 BTU/hr = 10,000 BTU/hr | ENERGY STAR |
10% of 5,000 BTU/hr is 500 BTU/hr (5,000 × 10%).
10% of 6,000 BTU/hr is 600 BTU/hr (6,000 × 10%).
A heavily shaded 150 sq ft bedroom should start on 5,000, then drop 10% to 4,500 BTU/hr. A very sunny 150 sq ft room should start on 6,000, then add 10% to 6,600 BTU/hr. On the 6,000 row, that sun swing is 600 BTU/hr, the same figure as the per-person adder, but they are different adjustments: one is 10% of the row, the other is 600 BTU/hr for each person beyond two.
One extra person on the shaded path is 5,000 + 600 = 5,600 BTU/hr, and you would still have started from the lower row because of the shade. One extra person on the sunny path is 6,000 + 600 = 6,600 BTU/hr. If this 150 sq ft space is actually a kitchen, add 4,000 after the row is chosen: 9,000 BTU/hr from 5,000, or 10,000 BTU/hr from 6,000. That kitchen case is worked in full on the kitchen air conditioner page.
The published chart is based on an 8-foot ceiling. ENERGY STAR's higher-ceiling note is a capacity step, not a percent: "If you have higher ceilings, you may want to select a room air conditioner with a higher CADR."
Buying the 6,000 row for a shaded room that belongs on 5,000 is the oversizing mistake in miniature. A unit that is too big cools the room before it removes humidity, and ENERGY STAR's result is that "cool, moist air will make the room feel damp and clammy."
If a window unit is a poor fit for a room this small, the ductless path is the mini-split room size guide.
6,000 BTU window air conditioners on Amazon Window air conditioner insulation foam on Amazon
Related questions
- What size air conditioner for a 200 sq ft room
- What size air conditioner for a 250 sq ft room
- What size air conditioner for a kitchen
All of these questions are listed on the topic map.
Sources
- ENERGY STAR, Room Air Conditioners — https://www.energystar.gov/products/room_air_conditioners — accessed Oct 2, 2026.
Frequently asked questions
Does a 150 sq ft room need 5,000 or 6,000 BTU/hr?
Both rows name 150 sq ft. 100 up to 150 sq ft is 5,000 BTU/hr, and 150 up to 250 sq ft is 6,000 BTU/hr. Heavy shade is the reason to stay on 5,000. A very sunny room, or more than two people in the room regularly, is the reason to start at 6,000.
How do the shade and sun adjustments change a 150 sq ft room?
Reduce capacity 10% for a heavily shaded room and increase it 10% for a very sunny room. Ten percent of 5,000 is 500, so a shaded room that starts on the lower row lands at 4,500 BTU/hr. Ten percent of 6,000 is 600, so a sunny room that starts on the higher row lands at 6,600 BTU/hr.
What if more than two people use this room, or it is a kitchen?
The chart already covers up to two people. Each person beyond two adds 600 BTU/hr, so one extra person on the 6,000 row is 6,600 BTU/hr. A unit used in a kitchen adds 4,000 BTU/hr: 6,000 + 4,000 = 10,000 BTU/hr. The kitchen page works that adder on its own.
Can I use this chart for a central air conditioner?
No. This is a room air conditioner chart, and it assumes an 8-foot ceiling. A whole-house central system should get a load calculation on the HVAC load calculator. If the ceiling is higher than that 8-foot basis, ENERGY STAR says you may want a room air conditioner with a higher CADR.