HVAC Size Calculator
Size an air conditioner or heat pump in BTU and tons from square footage, climate, ceiling height, insulation, sun, and occupancy.
How to use this hvac size calculator
Oversized AC short-cycles, never dehumidifies, and still costs more. Undersized AC runs forever on the hottest day. A Manual J calculation is what contractors should use; this HVAC size calculator is a planning estimate using climate, envelope, and occupancy.
A ton is 12,000 BTU/hr. Old rules like “1 ton per 500 sq ft” ignore insulation and glass. Replace the whole matched system when you can — a new condenser on an old coil wastes efficiency. Duct leaks can eat 20% of the capacity you just paid for.
Formula
Worked example
An 1,800 sq ft mixed-climate house with 8 ft ceilings and average insulation often lands near 3 tons — but a leaky, glassy home can need more.
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Frequently asked questions
How many BTU per square foot?
Roughly 20–32 BTU/sq ft for cooling depending on climate and shade. This tool uses 20–32 by climate, then adjusts.
How many square feet per ton?
Often 450–600 sq ft per ton. Do not size from that alone.
What is a Manual J?
The ACCA room-by-room load calculation. Ask your installer for it before you sign.
Can I round up a half ton “to be safe”?
Usually no. Extra capacity is worse for humidity than a slightly small unit with good ducts.
Does this size a furnace too?
It is cooling-oriented. Heating in cold climates needs a separate heat-loss calc; heat pumps still start from this cooling load.
How many square feet per ton of AC?
A rough rule is 450–600 sq ft per ton. Insulation, glass, climate, and occupancy move that number—this tool adjusts for them.
Is a Manual J better?
Yes. A Manual J is the contractor-grade room-by-room load. Use this HVAC size calculator to plan, then insist on Manual J before you buy.
Results are estimates for informational purposes and are not financial, legal, or professional advice. Last reviewed 2026-08-20.