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Science & Engineering Calculator
BTU Calculator
Estimate the BTU per hour needed to heat or cool a room from its dimensions, ceiling height, insulation, sun exposure, climate and occupancy.
BTU room size calculator
Use 8 ft or 2.4 m for a typical room.
Recommended capacity–
Cooling tons–
Approx. kilowatts–
Room area–
Enter the room details and calculate the estimated BTU/h capacity.
BTU formula used
This estimator starts from a common room sizing rule and adjusts it for ceiling height, insulation, sun exposure, climate and extra occupants.
Base BTU/h = room area in square feet x 20 x (ceiling height / 8)
Adjusted BTU/h = base BTU/h x insulation factor x sun factor x climate factor + occupant and kitchen adjustments
For air conditioners, 12,000 BTU/h is approximately 1 cooling ton. For power comparison, 1 kW is approximately 3,412 BTU/h.
How to use the BTU result
- Round up slightly if the room is sunny, poorly insulated or has many electronics.
- A unit that is much too large can short-cycle and remove less humidity.
- Open floor plans, staircases and connected rooms may need a whole-zone estimate instead of one room.
- Use this calculator as a planning estimate, then compare it with HVAC product guidance.
BTU Calculator FAQ
What does BTU mean?
BTU means British thermal unit. HVAC capacity is often shown as BTU per hour, which describes how much heat a system can move in one hour.
How many BTU do I need per square foot?
A common starting point is about 20 BTU per square foot, then adjusted for ceiling height, insulation, climate, sun and room use.
Is this calculator for heating or cooling?
It can be used as a room capacity estimate for both heating and cooling, but final equipment sizing should follow manufacturer and professional HVAC guidance.
Why does ceiling height matter?
A taller room contains more air volume, so the same floor area usually needs more heating or cooling capacity.
What is one ton of cooling?
One cooling ton is 12,000 BTU per hour.
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