Cooling Size Calculator
Enter the room's floor area and ceiling height, how sunny it is, how many people use it and whether it has a kitchen. The calculator breaks the cooling load into its parts and gives BTU an hour, kW and tons.
- Cooling load
- kW and tons
- Load breakdown
Very sunny means large south or west facing windows.
Each part of the room adds to the heat to remove. Start at about 20 BTU an hour per square foot for an 8 ft ceiling. A 300 sq ft room needs about 6,000 BTU an hour, or 1.76 kW. Sun adds 10%, each extra person 600 BTU and a kitchen 4,000.
Cooling load chart
8 ft ceiling, 2 people. Search for an area.
| Room (sq ft) | BTU/h | kW | Tons |
|---|---|---|---|
| 100 | 2000 | 0.59 | 0.17 |
| 150 | 3000 | 0.88 | 0.25 |
| 200 | 4000 | 1.17 | 0.33 |
| 300 | 6000 | 1.76 | 0.5 |
| 400 | 8000 | 2.34 | 0.67 |
| 500 | 10000 | 2.93 | 0.83 |
| 700 | 14000 | 4.1 | 1.17 |
| 1000 | 20000 | 5.86 | 1.67 |
Normal sun.
Room size and load
8 ft ceiling, very sunny, four people. Slide the floor area.
The bars show where the load comes from.
How to estimate cooling load
Room to BTU. Step through it.
Area
Square feet.
Close blinds on sunny windows. It can cut cooling load more than any other single step.
BTU, kW or tons
Cooling units. Compare them.
US rooms.
Metric.
Whole house.
Air conditioners in Europe are rated in kW, in the US in BTU or tons.
Before you buy
Cooling checks. Tick each item.
Tick each item as you go.
An oversized unit cools fast but leaves the room damp. Size close to the load.
What you get
Cooling load. Each tile explains one result.
BTU an hour.
Converted.
Converted.
Effect.
Effect.
Poor insulation or a top floor room can add 10 to 20% to the load.
Frequently Asked Questions
No question matches that search.
How do I calculate cooling load for a room?
Multiply the floor area in square feet by twenty, adjust for ceiling height and sun, then add for people and a kitchen.
How many BTU do I need per square foot?
About twenty for a normal room with an eight foot ceiling.
How do I convert BTU to kW?
Divide by three thousand four hundred and twelve.
What is a ton of cooling?
Twelve thousand BTU an hour, about three and a half kilowatts.
Does a kitchen need more cooling?
Yes, about four thousand BTU an hour more.
Do people add to cooling load?
Yes, about six hundred BTU an hour each beyond two.
Is a bigger air conditioner better?
No. An oversized unit short cycles and leaves the air humid.
Cool, not cold
Know the room's real load and choose a unit that matches it, for comfort without wasted power.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.