How accurate is this AC sizing calculator?

It is a transparent planning sanity check, not a room-by-room load calculation. It uses climate, conditioned area, ceiling height, envelope, windows and sun, leakage, occupancy, and ducts to produce a range. Final equipment sizing should use ACCA Manual J and Manual S.

How many square feet does a 3-ton air conditioner cool?

There is no reliable universal answer. Three tons is a nominal 36,000 Btu/h label, while the home load changes with climate, design temperature, humidity, glass, insulation, air leakage, ducts, and internal heat gains.

Why can an oversized AC be a problem?

An oversized system may satisfy the thermostat quickly and stop before removing enough moisture. It can also amplify airflow problems and cycle more often. Variable capacity helps modulation but does not remove the need for load and duct design.

Does a higher SEER2 rating always pay for itself?

No. Value depends on the price premium, climate runtime, electricity price, sizing, ducts, installation, and how long you own the system. This calculator shows the assumptions instead of promising a percentage.

What should an installed AC price include?

At minimum, compare both equipment model numbers, removal, labor, line-set work, ducts and airflow, electrical, condensate, controls, permit, startup measurements, parts warranty, and contractor labor coverage.

Free homeowner planning tool

AC sizing, energy & cost calculator

See whether the tonnage and installed price in your quote make sense.

What you get

✓ Btu/h and tonnage planning range
✓ State-based electricity comparison
✓ Scope-adjusted installed budget
✓ Quote warnings and contractor questions

Open result. No email gate. About three minutes.

Quick answer: floor area alone cannot select an air conditioner. This tool adds climate, ceilings, envelope, solar gain, leakage, occupants, and ducts to create a transparent planning interval. It helps challenge an unexplained quote; it does not replace a room-by-room ACCA Manual J or Manual S equipment selection.

Step 1 of 4

Home & climate

The facts that establish the starting point.

StateSets the climate region and current EIA state electricity price.

Conditioned floor areaft²Only include space served by this system.

Average ceiling heightft

Conditioned floors

Home type

Electricity rate (optional)¢/kWhLeave blank to use the April 2026 EIA residential average for your state.

Transparent methodology

How the calculator works

Capacity band

A climate-specific Btu/h-per-square-foot band is adjusted with bounded, visible factors. Unknowns widen the range rather than creating fake precision.

Energy comparison

Annual kWh uses nominal Btu/h × DOE regional equivalent cooling hours ÷ SEER2 ÷ 1,000, then applies your electricity price.

Installed scope

The budget starts with capacity and equipment tier, then names indoor equipment, ducts, electrical, line set, access, zoning, and permit uncertainty.

Important limitation: ACCA Manual J considers detailed design conditions, assemblies, fenestration, infiltration, ventilation, internal gains, and duct loads. Only ACCA-approved software can claim compliance. Use this result to ask better questions, not to order equipment.

Planning inputs, not market facts

What this planning model assumes

Reviewed July 10, 2026: the capacity starting points and installed budgets below are dated editorial planning assumptions created for this tool. They help a homeowner challenge a quote. They are not a contractor bid, appraisal, room-by-room load calculation, or promise of local availability.

Capacity starting bands

These editorial Btu/h-per-square-foot bands are the model's climate starting points before bounded adjustments for ceilings, shared walls, floors, envelope, solar exposure, leakage, ducts, and occupants.

Climate group	Btu/h per ft²
North	16–21
Mixed	18–24
Hot-dry	20–27
Hot-humid	22–28

Standard installed-cost starting bands

These editorial installed-cost bands cover the model's standard central-system base: outdoor equipment, standard removal, ordinary labor, and commissioning. Selected indoor equipment, ducts, electrical, line set, access, zoning, and permit uncertainty are added separately.

Nominal size	Editorial base band
1.5 tons	$4,500–$7,000
2 tons	$5,000–$7,800
2.5 tons	$5,500–$8,800
3 tons	$6,000–$9,800
3.5 tons	$6,800–$11,000
4 tons	$7,500–$12,500
4.5 tons	$8,000–$13,500
5 tons	$8,500–$14,500

Source and method boundary

DOE supplies the regional equivalent cooling-hour framework used in the energy comparison. EIA supplies the dated state electricity prices. ACCA and ENERGY STAR sources explain load calculation and quality-installation practice. Those organizations do not supply or endorse this tool's capacity starting bands or cost bands.

The editorial cost assumptions are not externally verified market prices. Local labor, equipment availability, taxes, incentives, code, access, contractor overhead, warranty coverage, and written scope can move a real proposal outside these bands. See the primary sources and data dates.

Capacity model review: July 10, 2026. Cost data version: 2026-07-10. Calculator method version: 2026.07.2.

Calculator FAQs

How accurate is this AC sizing calculator?: It is a transparent planning sanity check, not a room-by-room load calculation. It uses climate, conditioned area, ceiling height, envelope, windows and sun, leakage, occupancy, and ducts to produce a range. Final equipment sizing should use ACCA Manual J and Manual S.
How many square feet does a 3-ton air conditioner cool?: There is no reliable universal answer. Three tons is a nominal 36,000 Btu/h label, while the home load changes with climate, design temperature, humidity, glass, insulation, air leakage, ducts, and internal heat gains.
Why can an oversized AC be a problem?: An oversized system may satisfy the thermostat quickly and stop before removing enough moisture. It can also amplify airflow problems and cycle more often. Variable capacity helps modulation but does not remove the need for load and duct design.
Does a higher SEER2 rating always pay for itself?: No. Value depends on the price premium, climate runtime, electricity price, sizing, ducts, installation, and how long you own the system. This calculator shows the assumptions instead of promising a percentage.
What should an installed AC price include?: At minimum, compare both equipment model numbers, removal, labor, line-set work, ducts and airflow, electrical, condensate, controls, permit, startup measurements, parts warranty, and contractor labor coverage.

Primary sources and data dates

Calculator method version 2026.07.2. Editorial capacity and cost bands reviewed July 10, 2026.