Mini Split Square Footage Calculator
Calculate mini split BTU requirements from room square footage. A general rule is 20-30 BTU per square foot, but adjustments apply for ceiling height, sun exposure, insulation, and climate zone.
Mini Split Sizing Calculator
BTU per square foot rules
Standard rule: 20-30 BTU per square foot for cooling. A 400 sq ft bedroom needs 8,000-12,000 BTU - so a 9,000 BTU mini split is the typical pick.
Common mini split sizes: 6,000 BTU (covers 100-250 sq ft), 9,000 BTU (250-400), 12,000 BTU (400-550), 18,000 BTU (550-800), 24,000 BTU (800-1,200).
Adjustments to the rule
Add 10% for kitchen (heat from cooking). Add 10% for very sunny rooms. Add 10% for ceilings over 8 ft. Subtract 10% for shaded rooms or rooms with above-average insulation. Climate zones 1-2 (hot south) need higher BTU; zones 6-7 (cold north) need a heating-focused unit.
For a more accurate sizing, use Manual J load calculation (the industry standard). Most HVAC contractors offer this as part of a free quote.
Pro tips
Don't oversize
An oversized mini split short-cycles, doesn't dehumidify properly, and feels clammy. 20% oversized is okay; 50% oversized is a comfort problem.
Sunny west walls add load
Afternoon sun on a large west window can add 2,000+ BTU of solar gain. Account for room exposure when sizing.
Open floor plans need one bigger unit
A combined kitchen-living-dining isn't the sum of three small units - it's one large room. Size for the total square footage as one space.
Multi-zone for multiple rooms
For 3+ rooms, a multi-zone outdoor unit with separate indoor heads costs less per zone than 3 individual systems and gives independent room control.