Estimate what size central air conditioner your home needs before you talk to a contractor. Enter the square footage, ceiling height, climate, insulation, and window level, and the calculator converts the cooling load into tons (12,000 BTU/h each), rounded to the nearest half ton, along with a heating range and a table of what each standard size covers under your assumptions.
Cooling a single room with a window unit or mini-split? Use the BTU calculator, which shares the same method. If the new system needs a new circuit, the wire size calculator and voltage drop calculator help check the run.
Frequently asked questions
What size AC do I need for my square footage?
The traditional contractor rule is one ton of cooling (12,000 BTU/h) for every 400–600 square feet, depending on climate. With that rule a 2,000 sq ft house in a moderate climate needs about 40,000 BTU/h, or roughly 3.5 tons after rounding to the nearest half ton; the same house in a hot climate lands closer to 5 tons. This calculator also adjusts for ceiling height, insulation, and how much glass the house has. Remember that these rules are known to oversize, so use the result to sanity-check a quote, not replace a load calculation.
How many BTUs is one ton of air conditioning?
One ton of cooling equals 12,000 BTU per hour. The name dates back to ice-based cooling: it is the rate of heat absorbed by melting one ton of ice over 24 hours. So a 3-ton air conditioner removes about 36,000 BTU of heat per hour at its rated conditions, and a 5-ton unit about 60,000. Residential central systems are sold in half-ton steps from about 1.5 to 5 tons, although 4.5-ton units are uncommon. Loads larger than 5 tons are normally split across two systems.
Is a bigger air conditioner better?
No. An oversized AC reaches the thermostat setting quickly and shuts off before it has run long enough to pull moisture out of the air, so the house feels cool but clammy. The constant on-off short cycling also wastes energy and wears out the compressor sooner. A right-sized system runs longer, steadier cycles, dehumidifies properly, and is usually quieter. That is why HVAC designers use an ACCA Manual J load calculation rather than square footage, and why this tool rounds to the nearest half ton rather than always rounding up.
What is the difference between tons and SEER2?
Tonnage is capacity — how much heat the unit can remove per hour. SEER2 is efficiency — how much cooling it delivers per watt-hour of electricity over a typical season. A 3-ton unit cools the same house whether it is 14.3 SEER2 or 20 SEER2; the higher-rated one simply costs less to run. Since January 2023, the US minimum for most new split-system central air conditioners is 13.4 SEER2 in northern states and 14.3 SEER2 in the Southeast and Southwest. Pick the tonnage first, then decide how much efficiency is worth to you.
Why do I need a Manual J if this calculator gives me an answer?
Square-foot rules cannot see the things that actually drive your cooling load: window area and which way the windows face, shading, wall and attic insulation levels, air leakage, duct location, and your local design temperatures. ACCA Manual J accounts for all of them room by room, and building-science reviews of real homes often find loads of 1,000 or more square feet per ton — far less equipment than the rules of thumb suggest. Many jurisdictions require a Manual J for a new system permit, and any good contractor should provide one.