Formula and method
Area in ft² = length × width or entered area, converted if needed. Planning arithmetic in BTU/h = area in ft² × your entered BTU/h per ft². Thermal kW = BTU/h ÷ 3,412.141633.
Worked example
A 20 ft × 15 ft room is 300 ft². If you independently choose 20 BTU/h per ft² as a hypothetical assumption, arithmetic gives 6,000 BTU/h. The example factor is not sizing guidance.
Assumptions
There is no hidden fixed factor. The result changes directly with the factor you enter. Room insulation, windows, climate, orientation, air leakage, humidity, occupants, and other loads are not modeled.
Important limitations
This is only transparent planning arithmetic—not Manual J, a professional HVAC load calculation, or an equipment purchasing recommendation. Do not size or select heating/cooling equipment from this result alone.
Frequently asked questions
Is BTU/h the same as BTU? BTU is energy; BTU/h is a rate of heat transfer. Does this tool recommend an air-conditioner or heater size? No. A qualified load calculation is needed for that decision.
Privacy
Your inputs and result stay in this browser tab. This calculator does not send entered values to a server, save them in browser storage, or put them in the URL.