AC BTU Calculator
Calculate AC BTU and tonnage for any room — area, ceiling height, occupants, sun exposure and insulation. Find the right AC size in BTU/hr and tons.
Multiply length × width of the floor.
Cooling capacity
6,000 BTU/hr
0.5 tons
Recommended AC size
6,000 BTU/hr
window AC class
Room area
200 ft²
19 m²
Base capacity from the EnergyStar area chart, plus 1,000 BTU/hr for each foot of ceiling over 8 ft, 600 BTU/hr per person beyond two, and 4,000 BTU/hr for a kitchen. Sun and insulation adjust the total.
EnergyStar cooling capacity chart
Recommended cooling capacity by floor area, as published by EnergyStar.gov.
| Area (ft²) | Capacity (BTU/hr) | Approx. tons |
|---|---|---|
| 100–150 | 5,000 | 0.4 |
| 150–250 | 6,000 | 0.5 |
| 250–300 | 7,000 | 0.6 |
| 300–350 | 8,000 | 0.7 |
| 350–400 | 9,000 | 0.8 |
| 400–450 | 10,000 | 0.8 |
| 450–550 | 12,000 | 1 |
| 550–700 | 14,000 | 1.2 |
| 700–1,000 | 18,000 | 1.5 |
| 1,000–1,200 | 21,000 | 1.8 |
| 1,200–1,400 | 23,000 | 1.9 |
| 1,400–1,500 | 24,000 | 2 |
| 1,500–2,000 | 30,000 | 2.5 |
| 2,000–2,500 | 34,000 | 2.8 |
Last updated: May 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
Air-conditioner sizing in India follows a simple rule: bigger rooms and hotter climates need more cooling capacity. This calculator converts a room's floor area and ceiling height into the BTU rating and the equivalent tonnage you should look for on an AC's label. A typical 12 ft by 14 ft bedroom with an 8 ft ceiling comes to about 1,344 cubic feet, which works out to roughly 8,000–9,000 BTU or a 0.75–1 ton split AC. Use it when you are buying a new AC, moving into a rented flat with an unknown unit, or comparing quotes from dealers who quote in tons while the room is only measured in feet.
How to Use This Calculator
- Step 1: Measure the room length, width and ceiling height in feet.
- Step 2: Enter the three dimensions in the length, width and ceiling-height fields.
- Step 3: Select the sun exposure — sunny, average or shady — and the insulation quality of the room.
- Step 4: Read the required BTU per hour and the equivalent tonnage, then round to a standard AC size.
Worked Example
For a bedroom 12 feet by 10 feet with a 9-foot ceiling, that is 1,080 cubic feet of space. Choose average sun exposure and average insulation, and the tool estimates 27,000 BTU per hour, which is about 2.25 tons of cooling. That lands between the standard 2-ton and 2.5-ton split AC sizes sold in India. A sunny, poorly insulated room of the same size comes out higher, while a shady, well-insulated one comes out lower. Use the number as a starting point and confirm with the dealer for your city's climate.
Tips and Common Mistakes
- •Tip 1: Include the ceiling height — two rooms with the same floor area need different cooling if one has a 12-foot ceiling.
- •Tip 2: Sun-facing rooms in Indian summers run hotter in the afternoon; the sunny option adds roughly 10 percent over the average case.
- •Tip 3: Match the tonnage to the size bracket a dealer uses — 1, 1.5, 2 and 2.5 tons — rather than ordering an exact odd number.
- ✗Mistake 1: Entering the floor area as the volume — the tool expects length, width and height, so a 120 sq ft room needs all three figures.
- ✗Mistake 2: Oversizing by choosing the next biggest tonnage without checking; a much larger AC than needed cools poorly and runs in short cycles.
Frequently Asked Questions
What is BTU and how is it used for air conditioners?
BTU stands for British Thermal Unit — the energy needed to raise one pound of water by one degree Fahrenheit. Air conditioners are rated by how many BTUs they can remove per hour, and in India the same capacity is usually quoted in tons, where 1 ton equals 12,000 BTU.
How much AC capacity do I need for my room?
A typical rule of thumb is about 20–25 BTU per cubic foot of room volume, adjusted for sun exposure and insulation. For a 12 ft × 10 ft room with an 8 ft ceiling (960 cu ft) you need roughly 24,000 BTU, which is a 2-ton split AC. Hotter rooms with poor insulation need more.
What size AC do I need for a bedroom?
For an average Indian bedroom of about 120–150 sq ft with a 9–10 ft ceiling, a 1-ton (12,000 BTU) split AC is usually enough. Larger or south-facing rooms, or rooms with many windows, may need 1.5 tons. Enter your exact dimensions here to check.
What is the difference between 1 ton, 1.5 ton and 2 ton AC?
Tonnage measures cooling capacity: 1 ton = 12,000 BTU, 1.5 tons = 18,000 BTU and 2 tons = 24,000 BTU per hour. Bigger rooms and hotter climates need higher tonnage, but oversizing wastes electricity because the compressor cycles on and off more often.
How can I reduce the AC capacity I need?
Improve insulation, use curtains or blinds on sunny windows, seal gaps around doors and windows, and keep the room's heat sources (appliances, people count) in mind. A well-insulated room can often use one size smaller AC and still stay comfortable.
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