Enter the area you want to cool, the ceiling height, your climate, sun exposure and how many people use the space, and get a rule of thumb air conditioner size in BTU per hour, tons and kW.
Rule of thumb only. A Manual J load calculation is the proper way to size a central system.
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This ac tonnage calculator is for homeowners who want a first estimate before talking to an HVAC contractor, or who are checking whether a quote looks sensible. You get the cooling load in BTU per hour, the exact tons, the nearest half ton size and the capacity in kilowatts, in square feet or square meters.
How Do You Calculate AC Tonnage?
Multiply the floor area by a BTU per square foot figure for your climate, adjust for ceiling height, sun and people, then divide by 12,000. A 1,500 square foot home at 25 BTU per square foot, with 9 ft ceilings, strong sun and 4 people, needs about 47,606 BTU per hour, or 4 tons.
What Does Tonnage Mean for an Air Conditioner?
One ton of cooling is 12,000 BTU per hour, the heat needed to melt one short ton of ice in 24 hours.
tons = BTU/h ÷ 12,000
kW = BTU/h ÷ 3,412
A BTU, or British thermal unit, is the heat that warms one pound of water by 1 °F. Home central systems are sold in half ton steps, usually 1.5 to 5 tons. Outside the US, capacity is often given in kilowatts, and 1 ton equals about 3.52 kW. This tool rounds to the nearest half ton, so check the exact figure if you are close to the line.
How Many Square Feet Does a Ton of AC Cool?
As a rule of thumb, one ton of air conditioning cools about 400 to 600 square feet, depending on climate, insulation and sun.
The table uses 8 ft ceilings, normal sun and 2 people, with no other adjustments.
| Area (ft²) | Mild, 20 BTU/ft² | Warm, 25 BTU/ft² | Hot, 30 BTU/ft² |
|---|---|---|---|
| 400 | 8,000 (0.67 ton) | 10,000 (0.83 ton) | 12,000 (1 ton) |
| 600 | 12,000 (1 ton) | 15,000 (1.25 tons) | 18,000 (1.5 tons) |
| 1,000 | 20,000 (1.67 tons) | 25,000 (2.08 tons) | 30,000 (2.5 tons) |
| 1,500 | 30,000 (2.5 tons) | 37,500 (3.13 tons) | 45,000 (3.75 tons) |
| 2,000 | 40,000 (3.33 tons) | 50,000 (4.17 tons) | 60,000 (5 tons) |
| 2,500 | 50,000 (4.17 tons) | 62,500 (5.21 tons) | 75,000 (6.25 tons) |
The sun, people and kitchen rules come from ENERGY STAR guidance for room air conditioners: cut capacity by 10% for a heavily shaded room, add 10% for a very sunny one, add 600 BTU for each person beyond two, and add 4,000 BTU in a kitchen. For a single room or window unit, our BTU calculator gives a room by room figure.
Why Is Manual J the Proper Way to Size AC?
Manual J, published by the Air Conditioning Contractors of America (ACCA), is the proper sizing method because it adds up heat gain through every wall, window, roof and duct, instead of using floor area alone.
A rule of thumb cannot see your insulation, window size and direction, air leaks or local design temperatures, so two homes of the same size can need very different units. A US Department of Energy fact sheet on right sizing warns that an oversized unit costs more up front and cycles on and off, which can lead to poor humidity control, and tells homeowners to insist on a Manual J calculation. Ask contractors for a Manual J report and use this tool only as a sanity check. Better attic insulation and sealed air leaks lower the load, and the electricity cost calculator shows what the unit will cost to run.
Worked Example
A family in Georgia has a 1,500 square foot home with 9 ft ceilings, lots of afternoon sun and 4 people. With the Warm climate setting, the tool gives 47,606 BTU per hour, which is 3.97 tons, so the nearest size is 4 tons, about 13.95 kW. A single 300 square foot kitchen in a mild climate with 8 ft ceilings and 2 people gives 10,000 BTU, or 0.83 tons, rounded to a 1 ton unit. In metric, a 46.5 m² room at 2.4 m, hot climate and heavy shade comes to about 13,301 BTU, or 1.11 tons.
How Do You Use the AC Tonnage Calculator?
Pick units and area
Choose square feet or square meters and type the area you want to cool.
Set height, climate and load
Enter the ceiling height, then pick climate, sun, people and whether a kitchen is included.
Read the AC size
The big number is the nearest half ton size, with the exact BTU and tons below.
Check BTU and kW
The boxes show BTU per hour, exact tons, cooling kW and BTU per unit of area.
Frequently Asked Questions
How many BTU is a 3 ton AC?
A 3 ton air conditioner is 36,000 BTU per hour, because each ton is 12,000 BTU per hour. In metric that is about 10.6 kW of cooling capacity.
What size AC do I need for 2,000 square feet?
By rule of thumb, 2,000 square feet needs about 3.3 to 5 tons, or 40,000 to 60,000 BTU per hour, depending on climate. A Manual J calculation for your actual home often lands lower if it is well insulated.
Is a bigger air conditioner better?
No. An oversized unit cools the air quickly and shuts off before it removes much humidity, so rooms feel clammy. Frequent on and off cycles also waste energy and shorten the life of the compressor.
Does ceiling height affect AC size?
Yes. A higher ceiling means more air to cool. This tool scales the load by height ÷ 8 ft, so a 10 ft ceiling adds 25% compared with a standard 8 ft ceiling.
How much does each person add to the cooling load?
ENERGY STAR guidance adds about 600 BTU per hour for each person beyond two who regularly uses the room, because people give off body heat. Four people add 1,200 BTU per hour.
How do I convert AC tons to kW?
Multiply tons by 3.517 to get kilowatts of cooling. A 2 ton unit is about 7 kW and a 4 ton unit is about 14 kW. This is cooling output, not the electricity the unit draws.
Sources and Further Reading
- ENERGY STAR: Room air conditioners, sizing guidance
- ACCA: Manual J residential load calculation
- US Department of Energy (NREL): Right-size heating and cooling equipment fact sheet
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Last reviewed: October 2026