Mini-Split Sizing Calculator

A ductless mini-split serves one zone, so sizing a head starts with the same area rule the whole industry uses: roughly `20` BTU/hr per square foot of floor in a mild climate, rising toward `25` in a moderate one and `30` where the head also carries a cold heating season. Multiply your room area by that factor to get the cooling load the head must cover.

Manufacturers stock heads in fixed capacities — `6,000`, `9,000`, `12,000`, `15,000`, `18,000`, `24,000`, `30,000`, and `36,000` BTU/hr — so the calculator rounds your load up to the smallest head that meets it. A `400` square-foot room in a moderate climate needs about `10,000` BTU/hr, which a `12,000` BTU head covers comfortably.

Bigger is not better with mini-splits. An oversized head short-cycles: it blasts to temperature, shuts off, and never runs long enough to wring humidity out of the air, leaving the room cold and clammy. Modern inverter heads modulate well, but you still want the smallest head that carries the load. For a whole house, or a room with heavy sun or cathedral ceilings, a Manual J load calculation is the definitive sizing before you buy.