BTU Calculator
Calculate heating and cooling BTU requirements for any room based on dimensions and climate conditions.
BTU / Hour Required
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Tons of AC
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Recommended Unit
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What is BTU Calculator?
The BTU Calculator estimates the heating or cooling capacity needed for a room. BTU (British Thermal Unit) is the standard measure of thermal energy. Matching your HVAC unit's BTU rating to your room's requirements ensures efficient comfort without wasting energy.
How to use
- 1 Select the mode: Heating or Cooling.
- 2 Enter the room length, width, and ceiling height in feet.
- 3 For heating, enter the desired inside temperature and the coldest expected outside temperature.
- 4 For cooling, the calculator uses the standard 20 BTU per square foot rule.
- 5 Click Calculate to see the BTU requirement, AC tonnage, and recommended unit size.
Formula
Example calculation
A 15 × 20 ft room with 9 ft ceilings, inside 70°F, outside 10°F (ΔT = 60°F): BTU = 15 × 20 × 9 × 60 × 0.133 = 21,546 BTU/hr ≈ 1.8 tons.
Frequently asked questions
What is a BTU?
A British Thermal Unit is the amount of heat needed to raise one pound of water by one degree Fahrenheit. HVAC systems are rated in BTU/hr.
How many BTU per square foot for cooling?
A common rule of thumb is 20 BTU per square foot for average ceiling heights and climates. Sunny rooms, high ceilings, or hot climates may need more.
What is a 'ton' of air conditioning?
One ton = 12,000 BTU/hr. It originates from the cooling effect of melting one ton of ice over 24 hours.
Should I round up or down when buying an AC unit?
Round up to the next standard unit size (e.g., 1.5 ton, 2 ton). Undersized units run constantly; oversized units cycle too frequently and leave humidity behind.
Does insulation affect the BTU requirement?
Yes — poor insulation, single-pane windows, and air leaks significantly increase the BTU needed. This calculator provides a baseline estimate; a Manual J load calculation is more precise.