Mini split sizing
What size mini split do I need?
3-step calculator Based on ACCA Manual J (8th Edition) Reviewed by the WhatSize editorial team
Last reviewed June 2026 • Sources: ACCA Manual J, AHRI Directory, ENERGY STAR
Quick answer
Mini split size is measured in BTU and depends on room square footage, ceiling height, climate zone, and sun exposure. A 400 sq ft bedroom needs ~9,000 BTU; a 1,000 sq ft open living space needs 18,000-24,000 BTU. The 3-step wizard below applies ACCA Manual J (8th Edition) to your inputs.
How big is your room?
We'll adjust for ceiling height and room type in the next step.
Where is it located?
Room type and climate zone affect cooling needs.
Click a region on the map below:
Based on ACCA Manual J, 8th Edition (Load Calculation)
How we picked these products
Each product below is verified to meet or exceed your calculated spec. We sort by verified specifications first, then by availability and customer reviews. We never recommend a higher-priced product for a higher commission. Read our product recommendation policy.
Disclosure: WhatSize Appliance earns a commission when you buy through Amazon links. This doesn't affect which products we recommend. Read our full disclosure.
Got a result that doesn't match your situation?
Adjust your inputs above and re-run the calculator. Most users find their spec falls within 1-2 sizes of the recommendation.
Formula
BTU = Sq Ft × Climate Factor(18-28) × Room Factor(0.85-1.6) × Sun Factor(0.95-1.15) × Ceiling Factor
→ ACCA Manual J 8th Ed. simplified cooling-load calculation
About this calculation
This is a simplified sizing tool based on published industry standards, not a full professional audit. Critical applications (electrical, HVAC, flooding prevention) require site evaluation by a licensed contractor.
Accuracy depends on your input — subjective factors like dampness level or insulation quality are estimates. Our formulas include a safety buffer that may result in oversizing for some situations (slightly higher cost, but safer than undersizing).
Local variables (climate zone, altitude, insulation levels, building codes) can affect real-world sizing needs. Standards are re-checked quarterly — see our Editorial Policy.
Common scenarios for mini split sizing
If your situation matches one of these, jump straight to a detailed guide:
Frequently asked questions
How many BTU do I need per square foot?
Rule of thumb: 20 BTU per sq ft for well-insulated homes, 25 BTU for moderate climates, 30-35 BTU for hot climates or poor insulation. A 400 sq ft room typically needs 9,000-12,000 BTU. The ACCA Manual J 8th Edition load calculation is more accurate.
What size mini split for hot climates like Florida?
Florida, Texas, Arizona, and similar cooling-dominant climates need 30-35 BTU per sq ft. A 500 sq ft room in Miami typically needs a 15,000-18,000 BTU mini split. Add 10-15% for west-facing windows, attic heat gain, or kitchen heat load.
Do I need a bigger mini split for high ceilings?
Yes. For ceilings over 8 feet, multiply the base BTU by (ceiling height ÷ 8). A room sized for 12,000 BTU with 10 ft ceilings actually needs 15,000 BTU. Vaulted ceilings above 12 ft usually need a full ACCA Manual J calculation.
Can a mini split cool more than one room?
Multi-zone mini splits can serve 2-5 rooms from one outdoor compressor. Each indoor head is sized for its own room per Manual J. The total compressor capacity should exceed the sum of individual room needs by 10-15% for simultaneous peak load.