Mini Split Sizing Calculator
Find the right mini-split BTU size for a single room.
Enter your room's square footage and whether it gets heavy sun to estimate the BTUs a ductless mini-split needs, plus the nearest standard unit size (9k, 12k, 18k, 24k, or 36k BTU).
How it works
Mini-splits are sized at roughly 25 BTU per square foot, adjusted up about 10% for very sunny rooms. Round up to the next standard size — but avoid badly oversizing, since an oversized unit short-cycles and dehumidifies poorly.
Frequently asked questions
What size mini split do I need?
Allow about 25 BTU per square foot. A 500 sq ft room needs roughly 12,500 BTU, so an 18,000 BTU unit is the nearest standard size up.
What are common mini split sizes?
Single-zone units typically come in 9,000, 12,000, 18,000, 24,000, and 36,000 BTU capacities.
Is it bad to oversize a mini split?
Yes — an oversized unit short-cycles, wastes energy, and leaves humidity behind. Size close to the load rather than rounding up aggressively.
What size mini split for 1,000 sq ft?
About 25,000 BTU at the standard 25 BTU per square foot — between a 24,000 and 36,000 BTU unit. Good insulation and a mild climate favor the 24,000; lots of sun or an open layout favors sizing up.
Is this calculator free and private?
Yes. Every CubicCabin calculator runs entirely in your browser, so the numbers you enter are never uploaded or stored. There's no sign-up, no limits, and it keeps working even if you lose connection after the page loads.