Sizing an air conditioner
Air conditioners are rated in BTU per hour — the amount of heat they can move out of a room. A widely used rule of thumb is about 20 BTU per square foot of floor area for cooling. This tool converts your room to square feet, multiplies by that figure, and adjusts for how sunny the room is and how many people use it, since both add heat.
Why getting the size right matters
An undersized unit runs constantly and never quite cools the room; an oversized one cools too fast, cycles on and off, and leaves the air damp and clammy because it doesn't run long enough to remove humidity. Matching capacity to the room gives steady, efficient comfort.
Adjust for your conditions
The 20-per-square-foot figure assumes average ceilings and insulation. Rooms with tall ceilings, lots of glass, a kitchen, or heavy sun need more; well-shaded, well-insulated rooms need less. The editable BTU rate and the sun and occupant options let you tune the estimate to your space.
Frequently asked questions
How many BTU do I need per square metre?
Roughly 215 BTU per square metre at the common 20-per-square-foot rate. The tool converts automatically when you choose square metres.
What is a BTU in kilowatts?
About 3,412 BTU per hour equals 1 kilowatt. The note shows the approximate kW so you can match it to units sold in kW.