AC BTU
AC BTU SIZING
BTU ≈ ft² × 20 × adj
ft²
ppl
RESULT
—
FILL IN ABOVE
Rule of thumb. For tight specs use Manual J. Add 600 BTU/person above 2.
About this calculator
This BTU calculator gives a quick rule-of-thumb cooling load for sizing an air conditioner. The base rule is 20 BTU per square foot of room area, adjusted for sun exposure (±10%) and adding 600 BTU per occupant above two. For tight specs in commercial or unusual residential spaces, an HVAC contractor should run a Manual J load calculation. 12,000 BTU/hr equals one ton of cooling.
Common questions
How many BTUs do I need per square foot?
Rule of thumb: 20 BTU per ft² for cooling, adjusted for sun exposure (±10%) and occupancy (+600 BTU per person above 2). Heating loads vary more by climate — 30–60 BTU/ft² in southern US, 40–80 in northern.
What size AC unit for a 1,500 sq ft house?
Roughly 30,000 BTU = 2.5 tons. But whole-house sizing should always use Manual J load calculation — not square footage rules — because insulation, windows, and exposure matter more than size. Get a contractor's Manual J for new installs.
Is bigger AC better?
No. Oversized AC short-cycles — kicks on, cools fast, kicks off without removing humidity. Result: cold and clammy room. A right-sized unit runs longer cycles, dehumidifies properly, and uses less energy.