Heating & Cooling
Furnace Size Calculator
Estimate the BTU input rating for a gas furnace from square footage, climate zone and efficiency.
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Heating & Cooling
AC Ton Calculator
Estimate how many tons of cooling your home or room needs. The result adjusts for climate, ceiling height, sun exposure and the number of people in the space.
What is a ac ton calculator?
Air conditioners are sized in tons: one ton removes 12,000 BTU of heat per hour. This calculator estimates the cooling load and rounds up to the nearest half-ton, the step most residential equipment comes in.
How does it work?
Area × a climate factor gives a base load, scaled for ceilings above 8 ft and adjusted ±10% for sun. Extra occupants add 600 BTU/h each. The total ÷ 12,000 gives tons. Planning heating too? See the Furnace Size Calculator. A new roof with better insulation or a lighter colour can reduce cooling load — compare with the Roof Square Footage Calculator if you are doing both.
What information is needed?
- Floor area of the cooled space
- Your summer climate
- Ceiling height
- Typical number of occupants
- How sunny the space is
How to use the AC Ton Calculator
- Measure the area to be cooled.
- Choose your climate and sun exposure.
- Enter ceiling height and occupants.
- Select Calculate.
The formula
In plain terms, here is the calculation the tool runs:
BTU/h = Area × Climate × (H ÷ 8) × Sun + 600 × (People − 2)
Tons = BTU/h ÷ 12,000
- Climate
- 20–30 BTU/h per sq ft
- Sun
- 0.9 shaded, 1.0 average, 1.1 sunny
- 12,000
- BTU/h in one ton of cooling
Worked example
Example
A 1,500 sq ft home in a moderate climate, 8 ft ceilings, four people, average sun.
- 1,500 × 25 × 1 × 1 = 37,500
- + 600 × 2 extra people = 38,700 BTU/h
- 38,700 ÷ 12,000 = 3.23 tons
Look at a 3.5-ton system.
Frequently asked questions
Why round up to half a ton?
Residential condensers are sold in half-ton steps. Rounding up slightly is safer than rounding down, but avoid going a full ton over.
Is bigger better for AC?
No. An oversized unit cools quickly but runs short cycles and removes less humidity, so the house feels clammy.
What about a single room?
Enter just that room’s area. A 12 × 15 room in a moderate climate needs about 4,500–5,000 BTU/h.
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