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Air Conditioner Size Calculator

Estimate the cooling capacity a space needs in BTU/h and tons, adjusted for climate, insulation, glazing and occupancy.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Cooling capacity required

21527.82 BTU/h

Low confidence

A screening estimate, not a design. Equipment should be selected from a room-by-room load calculation (ACCA Manual J in North America, MCS/CIBSE in the UK, AS/NZS in Australia) before anything is ordered.

Tons of refrigeration
1.79 tons
Kilowatts
6309.18 kW
Envelope and solar
21527.82 BTU/h
Occupants beyond two
0 BTU/h
Kitchen
0 BTU/h

For the dimensions entered, expect a cooling capacity required of 21528 BTU/h. Of the working steps, envelope and solar dominates at 21528 BTU/h. Note that floor area and regular occupants sit at the edge of the range this calculator was checked against, so treat the output as indicative rather than settled. The confidence rating here is low. Get the figure confirmed by a supplier or a qualified trade before committing to it. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Add the equipment this sizes

This result is a specification — 21,527.821 BTU/h — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • ACCA Manual J (8th ed.) — residential load calculation. This page is a screening approximation of it, not an implementation.
  • 1 ton of refrigeration = 12,000 BTU/h (ASHRAE Terminology)
  • ACCA Manual S — equipment selection should follow the calculated load, not floor area alone

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Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Still deciding? Heat Pump vs Air Conditioner — the factors that actually differ, with no invented prices.

Frequently asked questions

Why is a bigger air conditioner worse?
Because cooling and dehumidifying are different jobs. An oversized unit drops the air temperature fast, satisfies the thermostat and stops — before it has run long enough to condense much moisture out. The result is a house that is cold and clammy, with the compressor short-cycling, which wears it out and wastes energy. Correct sizing runs longer at lower capacity, which is what actually removes humidity.
How does this differ from a real Manual J?
A Manual J is room by room and uses the actual window areas, orientations and shading; the U-value of every wall, roof and floor assembly; a measured or assumed infiltration rate; duct location and leakage; and separate sensible and latent loads. This uses floor area with four adjustment factors. It is useful for a sanity check on a quote and is not a basis for ordering equipment.
What is a ton of cooling?
12,000 BTU/h — historically the rate of cooling from melting a ton of ice in a day. It is a capacity, not a weight. Residential systems are commonly 1.5 to 5 tons, and equipment is sold in half-ton steps, so the calculated figure gets rounded to the nearest available size.
Should I round up to the next size?
Usually down, or to the nearest. Manual S allows selecting up to about 15% above the calculated cooling load; beyond that the short-cycling and humidity problems start. Rounding up 'to be safe' is the exact instinct that causes most oversizing.