AC size calculator
Enter the room size and a few conditions. The page shows the cooling load in BTU per hour and the standard ton size to compare, from 0.75 ton upward.
- Tons and BTU
- Free, no sign-up
Runs in your browser. Nothing you type or open is uploaded. Free to use, no account. More everyday tools
How to use it
- Enter length, width and ceiling height.
- Set sun, top floor, people, kitchen and climate.
- Read the BTU per hour, the calculated tons and the next standard size.
A practical room estimate
The base is 125 watts per square metre of floor at a 2.7 m ceiling, then multiplied for sun, climate, a top-floor roof and the real ceiling height. Two people are included in the base. Each extra person adds 150 watts, and a kitchen in the room adds 1,200 watts. Watts convert at 3.412 BTU per hour per watt.
One ton of cooling is 12,000 BTU per hour. The suggested unit is the next standard size at or above the calculated load: 0.75, 1, 1.5, 2, 2.5, 3, 4 or 5 tons. A west-facing glass wall or a crowded kitchen can sit above this estimate, so an installer’s room-by-room load is the figure to buy on.
Private by design
Privacy
Everything runs in this page and stays on your device. The room details stay on this device.
This page also shows Google ads, which can use cookies. Privacy and cookies explains how.
Questions
How many BTU are in a ton?
One ton of refrigeration is 12,000 BTU per hour. A 1.5 ton unit is 18,000 BTU per hour.
What size is a 4 by 5 metre room?
At an average sun, a moderate climate, a 2.7 m ceiling and two people, the load is about 0.71 ton, so the standard size to compare is 0.75 ton.
Does a top-floor room need more?
Yes. The page adds 10% when the room is on the top floor, because the roof picks up heat.
What do the sun and climate choices change?
Little sun multiplies by 0.85 and a lot of sun by 1.20. Cool climate is 0.85, hot is 1.15 and very hot is 1.30. They stack with the ceiling-height factor.
What is included for people and a kitchen?
The base covers two people. Each person beyond that adds 150 watts. A kitchen in the same room adds 1,200 watts.