BTU Calculator
Updated Formulas shown
A 20 × 15 ft room (300 ft²) needs about a 7,000 BTU air conditioner under the ENERGY STAR chart. Very sunny rooms need about 10% more; kitchens add 4,000 BTU.
Air conditioner size
7,000 BTU/h
0.58 tons
- Room area
- 300 ft²
- Closest common AC sizes
- 8,000 or 10,000
Based on the ENERGY STAR room AC sizing chart: −10% for heavy shade, +10% for very sunny rooms, +600 BTU per person over two, +4,000 BTU for kitchens.
Quick reference
| Room area | BTU per hour |
|---|---|
| 100–150 ft² | 5,000 |
| 150–250 ft² | 6,000 |
| 250–300 ft² | 7,000 |
| 300–350 ft² | 8,000 |
| 350–400 ft² | 9,000 |
| 400–450 ft² | 10,000 |
| 450–550 ft² | 12,000 |
| 550–700 ft² | 14,000 |
| 700–1,000 ft² | 18,000 |
| 1,000–1,200 ft² | 21,000 |
| 1,200–1,400 ft² | 23,000 |
| 1,400–1,500 ft² | 24,000 |
| 1,500–2,000 ft² | 30,000 |
| 2,000–2,500 ft² | 34,000 |
Related calculators
- Electricity Cost CalculatorCalculate the cost to run any appliance per day, month and year from its wattage, hours of use and your electricity rate.
- Insulation CalculatorCalculate insulation batts or rolls for walls, attics and floors from area and bag coverage.
- Square Footage CalculatorCalculate square footage of rectangles, circles, triangles and trapezoids, with square yards, square meters, acres and cost.
Frequently asked questions
Is a bigger air conditioner better?
No. An oversized unit cools too fast and shuts off before removing humidity, leaving the room clammy and wasting energy.
Your business here? Sponsor this calculator from $13/week. See placements
Estimates only. Check quantities with your supplier or contractor before ordering.