Air Conditioner Size Calculator

Find the right AC tonnage for your home. Enter your climate zone and square footage to get an accurate system size recommendation in seconds.

Calculate Your AC Size

Not for mobile home systems. See mini splits for rooms under 400 sq ft. Select the region you live in according to the color keyed map below Select the system type needed for your home. Enter the approximate square footage of the area you need to heat or cool (minimum 600 sq. ft.). If your space is under 400 sq. ft., view our Mini Split options.
Click the Calculate System Size button.
US Regions

Disclaimer:

This calculator provides a general estimate of HVAC tonnage based on climate zone and square footage. It doesn't account for vaulted ceilings, insulation quality, building construction, window size and orientation, or local temperature extremes. Actual requirements vary considerably between homes, so we recommend having a licensed HVAC contractor perform a professional load calculation before purchasing.

Replacing an existing system? Stick with the same tonnage unless you've added square footage, experienced consistent comfort problems, or made major insulation upgrades since the original installation.

Our sales team brings over 40 years of industry experience and can help you work through the details. Contact us here or call 1-813-885-7999 .

  • System tonnage

AC Tonnage and BTU Calculator

AC Sizing Chart by Climate Zone

This quick-reference chart shows the approximate square footage each AC size can handle based on your climate zone. Hotter climates (Zone 1) require more cooling capacity per square foot than cooler regions (Zone 5).

AC Size Zone 1 Zone 2 Zone 3 Zone 4 Zone 5
1.5 Tons 600 - 900 sf 600 - 950 sf 600 - 1,000 sf 700 - 1,050 sf 700 - 1,100 sf
2 Tons 901 - 1,200 sf 951 - 1,250 sf 1,001 - 1,300 sf 1,051 - 1,350 sf 1,101 - 1,400 sf
2.5 Tons 1,201 - 1,500 sf 1,251 - 1,550 sf 1,301 - 1,600 sf 1,351 - 1,600 sf 1,401 - 1,650 sf
3 Tons 1,501 - 1,800 sf 1,501 - 1,850 sf 1,601 - 1,900 sf 1,601 - 2,000 sf 1,651 - 2,100 sf
3.5 Tons 1,801 - 2,100 sf 1,851 - 2,150 sf 1,901 - 2,200 sf 2,001 - 2,250 sf 2,101 - 2,300 sf
4 Tons 2,101 - 2,400 sf 2,151 - 2,500 sf 2,201 - 2,600 sf 2,251 - 2,700 sf 2,301 - 2,700 sf
5 Tons 2,401 - 3,000 sf 2,501 - 3,100 sf 2,601 - 3,200 sf 2,751 - 3,300 sf 2,701 - 3,300 sf

Why Proper AC Sizing Matters

Getting your air conditioner size right is one of the most important decisions you'll make when purchasing a new system. Too small, and your home won't cool properly on hot days. Too large, and you'll face a different set of problems that many homeowners don't anticipate.

The Oversizing Trap: An oversized AC short-cycles, turning on and off rapidly without running long enough to remove humidity. The result? A cold, clammy house, higher energy bills, and a compressor that wears out years before it should.

Decode Your Existing System Size

Manufacturers embed the BTU capacity in the model number of the outdoor unit. Look for a two-digit number like 24, 36, or 48. Divide that by 12 to get the tonnage (12,000 BTUs = 1 ton).

For example, model GSX140241K is a 2-ton unit. The "24" represents 24,000 BTUs. Divide by 12,000 and you get 2 tons.

24,000 BTUs ÷ 12,000 BTUs per ton = 2 tons

Use this reference to decode model numbers:

18 = 1.5 tons
24 = 2 tons
30 = 2.5 tons
36 = 3 tons
42 = 3.5 tons
48 = 4 tons
60 = 5 tons

Professional Load Calculations

Our online calculator provides a solid estimate, but a Manual J load calculation accounts for every variable: window orientation, insulation R-values, ceiling height, ductwork condition, and local design temperatures. We offer Manual J calculations with 1-2 day turnaround if you want engineering-grade precision.

Heating Capacity by Climate Zone

When sizing a furnace or heat pump, your climate zone determines how many BTUs you need per square foot. Colder regions require significantly more heating capacity than mild climates.

Zone 1

30-35 BTU/sq ft

Zone 2

35-40 BTU/sq ft

Zone 3

40-45 BTU/sq ft

Zone 4

45-50 BTU/sq ft

Zone 5

50-60 BTU/sq ft

Use the lower number if your home is well-insulated with modern windows. Use the higher number for older homes or those with single-pane windows and minimal insulation.

Sample Heating Calculation

A 2,000 sq ft home in Zone 3 with good insulation:

2,000 sq ft × 40 BTU/sq ft = 80,000 BTU required output

For gas furnaces, you need to account for efficiency. An 80% AFUE furnace with 100,000 BTU input produces:

100,000 BTU input × 0.80 efficiency = 80,000 BTU actual output

A 93% AFUE furnace with the same input rating produces 93,000 BTU of usable heat, potentially allowing you to downsize the equipment.

Insulation and Window Variables

Your home's construction dramatically affects heating and cooling loads. Two-story homes place less demand on downstairs equipment because the second floor acts as insulation. Homes with cathedral ceilings, large window areas, or poor air sealing will trend toward the higher end of sizing ranges. When uncertain, err toward well-insulated estimates for newer construction and poor-insulation estimates for pre-1980 homes.

Frequently Asked Questions

  • How do I calculate what size air conditioner I need?

    Start by determining your climate zone (1-5) based on your geographic location, then measure the square footage of the space you need to cool. As a general rule, you need approximately 1 ton of cooling capacity for every 400-600 square feet, with hotter climates requiring more capacity per square foot. Our calculator factors in both variables to give you an accurate recommendation.

  • What happens if I buy an AC that's too big for my home?

    An oversized air conditioner will short-cycle, meaning it turns on and off frequently without running long enough to properly dehumidify your home. This leads to a cold but clammy indoor environment, higher energy bills from constant startup cycles, and premature wear on the compressor. Proper sizing is critical for both comfort and equipment longevity.

  • How many BTUs are in a ton of air conditioning?

    One ton of air conditioning equals 12,000 BTUs per hour. This measurement dates back to the amount of heat needed to melt one ton of ice in 24 hours. So a 2-ton unit produces 24,000 BTUs, a 3-ton unit produces 36,000 BTUs, and a 5-ton unit produces 60,000 BTUs of cooling capacity.

  • How can I find the tonnage of my existing AC unit?

    Look at the model number on your outdoor condenser unit (not the serial number). Find a two-digit number like 18, 24, 30, 36, 42, 48, or 60 within the model string. Divide that number by 12 to get your tonnage. For example, if you see "24" in the model number, you have a 2-ton system (24,000 BTUs ÷ 12,000 = 2 tons).

  • Does insulation affect what size AC I need?

    Yes, significantly. Well-insulated homes with modern double-pane windows can often use a smaller system within the recommended range for their square footage. Older homes with poor insulation, single-pane windows, or excessive air leaks will need to size toward the higher end. Two-story homes typically need less capacity for the ground floor since the upper level provides additional insulation.

  • What's the difference between this calculator and a Manual J load calculation?

    Our online calculator provides a reliable estimate based on climate zone and square footage. A Manual J load calculation is an engineering-grade assessment that factors in window orientation, insulation R-values, ceiling height, ductwork efficiency, number of occupants, and local design temperatures. Manual J is more precise and recommended for new construction or when maximum efficiency is the priority.

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