Home energy · cooling
Room AC BTU sizing, with every adjustment shown.
Find the capacity ENERGY STAR's chart assigns to your floor area, then see each sun, occupant and kitchen adjustment added or subtracted.
Inputs
Capacity estimate
Worked example
A 350 sq ft bedroom is in the chart's 350 up to 400 sq ft row, which is 9,000 BTU/h. It is very sunny (+10% = +900), three people use it (one beyond two = +600) and it is not a kitchen. Total: 9,000 + 900 + 600 = 10,500 BTU/h, about 3.08 kW of cooling.
Formula, assumptions and source
Step 1: find the area row in ENERGY STAR's "Area to be cooled" chart. Step 2: apply the sun adjustment (shaded −10%, very sunny +10%) to that chart value. Step 3: add 600 BTU/h per person beyond two and 4,000 BTU/h for a kitchen. ENERGY STAR lists the adjustments but does not state their order; this tool applies the percentage to the chart value only, then adds the fixed amounts. The kW figure divides BTU/h by 3,412.
| Area (sq ft) | Area (m², approx.) | Capacity (BTU/h) |
|---|---|---|
| 100 up to 150 | 9.3 to 13.9 | 5,000 |
| 150 up to 250 | 13.9 to 23.2 | 6,000 |
| 250 up to 300 | 23.2 to 27.9 | 7,000 |
| 300 up to 350 | 27.9 to 32.5 | 8,000 |
| 350 up to 400 | 32.5 to 37.2 | 9,000 |
| 400 up to 450 | 37.2 to 41.8 | 10,000 |
| 450 up to 550 | 41.8 to 51.1 | 12,000 |
| 550 up to 700 | 51.1 to 65.0 | 14,000 |
| 700 up to 1,000 | 65.0 to 92.9 | 18,000 |
| 1,000 up to 1,200 | 92.9 to 111.5 | 21,000 |
| 1,200 up to 1,400 | 111.5 to 130.1 | 23,000 |
| 1,400 up to 1,500 | 130.1 to 139.4 | 24,000 |
| 1,500 up to 2,000 | 139.4 to 185.8 | 30,000 |
| 2,000 up to 2,500 | 185.8 to 232.3 | 34,000 |
The chart assumes an 8 ft ceiling. Metric input is converted at 1 m² = 10.764 sq ft. Chart and adjustments retrieved from ENERGY STAR on 2026-09-30; the page shows no revision date. This is a planning estimate: climate, insulation, windows and unit efficiency are not modeled.
Source: ENERGY STAR, Room Air Conditioners (sizing chart and adjustments)
FAQ
How many BTU do I need for a 300 square foot room?
The chart gives 8,000 BTU/h for 300 up to 350 sq ft, before adjustments.
Does a bigger air conditioner cool better?
Follow the chart plus its adjustments. This tool does not model oversizing, so treat the result as a planning figure.
What if my ceilings are taller than 8 feet?
ENERGY STAR gives no numeric correction, so none is applied; the result flags it so you can consider a larger unit.