BTU & AC Size Calculator
Estimate the cooling and heating BTU your room needs from area, ceiling, occupants, sun, insulation and climate zone. Runs 100% in your browser.
Runs locally in your browser — no upload, no trackingTry: Room area=150, Ceiling height=8, People usually in room=1, Room type=living, Sun exposure=avg, Insulation quality=avg, Climate zone (1–5)=3 → 3,000 BTU, 0.25 ton, 5,000 BTU window unit, 5,500 BTU
How to use
Enter your room area and adjust the other inputs to match the space. Press Calculate to see the cooling BTU, the tonnage, a recommended unit size and an estimate of the heating load. Everything runs locally in your browser.
Rule of thumb: start at 20 BTU per square foot, then add for people, sun and a hot climate, or trim for a shaded, well-insulated room. A 12,000 BTU unit equals one ton of cooling.
FAQ
How many BTU per square foot do I need?
A common starting point is 20 BTU per square foot of conditioned space. Add about 600 BTU for each person beyond two, 4,000 BTU for a kitchen, and adjust for sun, insulation and climate zone. The calculator does all of that for you.