BTU Calculator
BTU (British Thermal Unit) is the standard measure of heating and cooling capacity. This calculator estimates how many BTUs per hour you need based on your room size, insulation quality, and climate zone.
Enter Your Measurements
Results
How to Use This Calculator
- Enter the room's square footage.
- Enter ceiling height (8 feet is standard).
- Select your climate zone based on your region.
- Rate your insulation quality and sun exposure.
- Enter the number of people who regularly use the room.
How BTU Calculation Works
This calculator uses a rule-of-thumb method that multiplies your square footage by a climate-specific BTU factor, then adjusts for ceiling height, insulation quality, sun exposure, and occupant heat gain. Each person adds about 600 BTU/hr of body heat. The result is a sizing estimate for both cooling (AC tonnage) and heating (furnace MBH). For precise results, a Manual J calculation is recommended — this calculator provides a solid starting estimate.
Formula
BTU/hr = Sq Ft × Climate Factor × (Ceiling Height ÷ 8) × Insulation Factor × Sun Factor + (Occupants - 2) × 600. AC Tons = BTU/hr ÷ 12,000.