BTU Calculator
Calculate heating and cooling BTU requirements for your room or home. Determine the right AC tonnage and furnace size based on room dimensions, insulation, and climate.
Inputs
Results
Cooling Capacity Needed
10,000 BTU/hr
How to Use This Calculator
- Enter the room length, width, and ceiling height in feet.
- Select the ceiling type (standard, high, or vaulted) and insulation quality.
- Choose your climate zone and sun exposure to adjust the load estimate.
- Enter the total window area in square feet — more glass increases both heating and cooling loads.
- Read the cooling BTU/hr and AC tonnage to size an air conditioner, and heating BTU/hr to size a furnace.
How the result changes with Room Length
| Room Length | Cooling Capacity Needed |
|---|---|
| 15 | 9,000 BTU/hr |
| 38 | 17,000 BTU/hr |
| 67 | 28,000 BTU/hr |
| 91 | 37,000 BTU/hr |
What each input means
- Room Length
- Length of the room in feet.
- Room Width
- Width of the room in feet.
- Ceiling Height
- Height from floor to ceiling.
- Total Window Area
- Approximate total square footage of all windows in the room.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersRoom Length = 20, Room Width = 15, Ceiling Height = 9, Ceiling Type = 0 = 8 input(s) provided
- Calculate Cooling Capacity NeededCooling Capacity Needed10000 = 10000
- Calculate Heating Capacity NeededHeating Capacity Needed22000 = 22000
- Calculate AC Tonnage1 = 1
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.
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