ComfortSizer
Central air · heat pump

AC Tonnage Calculator

What size central AC or heat pump does your home need? Enter the square footage, pick your climate zone and insulation, and get a starting tonnage before you talk to installers.

sq ft
ft
Your climate zone

Insulation
Cooling load –tons
How we got this number

    100% private: the math runs in your browser and nothing is sent anywhere. Estimates for one room or open space up to 2,500 sq ft.

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    How the tonnage estimate works

    Central air conditioners and heat pumps are sold in tons: one ton removes 12,000 BTU of heat per hour. A quick, widely used way to estimate a whole home is cooling BTU per square foot, adjusted for climate:

    • Hot (zone 1): about 30 BTU per sq ft, roughly 400 sq ft per ton.
    • Warm (zone 2): about 25 BTU per sq ft, roughly 480 sq ft per ton.
    • Mild (zone 3): about 22.5 BTU per sq ft, roughly 530 sq ft per ton.
    • Cool (zone 4): about 20 BTU per sq ft, roughly 600 sq ft per ton.
    • Cold (zone 5): about 18 BTU per sq ft, roughly 670 sq ft per ton.

    We then adjust for insulation (+15% for a drafty older home, −10% for a tight newer one) and ceiling height, and round up to the next standard size: 1.5, 2, 2.5, 3, 3.5, 4 or 5 tons.

    Use this to plan, not to sign. Rules of thumb often oversize systems. Before you buy, ask the installer for a Manual J load calculation; it frequently comes out smaller than the rule of thumb.

    Why oversizing hurts

    An oversized central system cools the house in short bursts, so it never runs long enough to pull moisture out of the air. You get a cold, clammy house, more wear on the compressor and higher bills. Undersizing shows up as a system that cannot keep up on the hottest afternoons.

    FAQ

    Questions

    How many tons of AC do I need for 2,000 square feet?
    With this rule of thumb and average insulation: 5 tons in a hot climate (zone 1), about 4.2 tons in a warm one (so a 4.5-ton system), 3.75 tons in a mild climate (4-ton system), 3.3 tons in a cool climate (3.5-ton system) and 3 tons in a cold one. A Manual J calculation often gives less.
    How many square feet does a 3-ton AC cool?
    Roughly 1,200 sq ft in a hot climate, 1,440 in a warm one, 1,600 in a mild climate, 1,800 in a cool climate and 2,000 in a cold one, with average insulation and 8 ft ceilings.
    How many BTU is a ton of air conditioning?
    One ton equals 12,000 BTU per hour. A 2.5-ton system is 30,000 BTU and a 4-ton system is 48,000 BTU.
    What is the largest residential central AC?
    Residential condensers usually top out at 5 tons. Bigger homes use two systems or zoned equipment.
    Is this the same as a Manual J?
    No. Manual J accounts for windows, orientation, insulation, air leakage and ducts room by room. This calculator gives a quick estimate to help you plan and compare quotes.