Mini-Split Sizing Calculator & BTU Guides
Work out what size mini-split you need — enter your room, ceiling, climate and sun to get the exact BTU capacity and the matching 9k–36k unit size.
btuwise’s sizing tools turn your room into a BTU number you can actually shop with. The mini-split BTU calculator takes your square footage, ceiling height, US climate zone, sun exposure, insulation and occupancy and returns the exact cooling-and-heating capacity you need, then names the standard size — 9,000, 12,000, 18,000, 24,000 or 36,000 BTU (¾ to 3 tons) — and whether a single- or multi-zone system fits. The BTU-per-square-foot logic is shown in the open, not hidden, so you can see why the number is what it is. Oversize a mini-split and it short-cycles, cools unevenly and wastes money; undersize it and it never keeps up. Every figure is a planning estimate — confirm the final load with a licensed HVAC pro before you buy or install.