BTU Calculator
Heating and cooling capacity a room needs.
Enter your values
Enter the room area in sq ft.
Enter the ceiling height in ft.
Choose one of: Heavily shaded, Average, Very sunny.
Choose one of: Well insulated, Average, Poor.
Enter the people usually in the room you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Cooling capacity needed
- 8,000 BTU/hr
- In tons of cooling
- 0.67
- Heating capacity (rough)
- 12,000 BTU/hr
- In kilowatts
- 2.34 kW
Quick answer
A rough baseline is 20 BTU per square foot for cooling, adjusted for ceiling height, sunlight and insulation quality.
BTU ≈ area × 20 × adjustment factors
At a glance
| What it does | Heating and cooling capacity a room needs. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Room area, Ceiling height, Sun exposure, Insulation, People usually in the room |
| Main output | Cooling capacity needed |
| Formula | BTU ≈ area × 20 × adjustment factors |
| Cost | Free — no sign-up, no download |
How to use the BTU Calculator
- 1Enter the room area and ceiling height.
- 2Pick sun exposure and insulation quality.
- 3Read the BTU capacity to shop for.
Inputs explained
- Room area(sq ft)
- Enter the room area in sq ft.
- Ceiling height(ft)
- Enter the ceiling height in ft.
- Sun exposure
- Choose one of: Heavily shaded, Average, Very sunny.
- Insulation
- Choose one of: Well insulated, Average, Poor.
- People usually in the room
- Enter the people usually in the room you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Room area400 sq ft
- Ceiling height8 ft
- Sun exposureAverage
- InsulationAverage
- People usually in the room2
Results
- Cooling capacity needed8,000 BTU/hr
- In tons of cooling0.67
- Heating capacity (rough)12,000 BTU/hr
- In kilowatts2.34 kW
Frequently asked questions
Is a bigger unit better?
No. An oversized AC short-cycles, cooling fast without removing humidity, which leaves the room clammy.
How many BTU is a ton?
12,000 BTU per hour — the rate at which a ton of ice melts in 24 hours.
What do I need to enter into the BTU Calculator?
Just 5 values: room area, ceiling height, sun exposure, insulation, people usually in the room. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the BTU Calculator work out the answer?
A rough baseline is 20 BTU per square foot for cooling, adjusted for ceiling height, sunlight and insulation quality. It applies the formula BTU ≈ area × 20 × adjustment factors and shows the working so you can check each step by hand.
Is the BTU Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.