HVAC Tonnage Calculator by Square Foot
Rough air conditioner size for a home.
Enter your values
ⓘ Live results
Results
- Estimated load
- 46,800 BTU/h
- Tonnage
- 3.9 tons
- Round to
- 4 tons
- Airflow at 400 CFM/ton
- 1,560 CFM
- Caution
- Confirm with a Manual J before buying
Quick answer
A rough estimate is 20-30 BTU per square foot, but a Manual J load calculation is always more accurate.
tons = area x BTU per sq ft / 12000
How to use the HVAC Tonnage Calculator by Square Foot
- 1Enter conditioned floor area, climate and insulation quality.
- 2Round to the nearest half ton — equipment only comes in those steps.
- 3Get a Manual J load calculation before purchase; oversizing hurts humidity control badly.
Worked example
Using the values the calculator loads with:
Inputs
- Home area1800 sq ft
- ClimateMixed
- InsulationAverage
Results
- Estimated load46,800 BTU/h
- Tonnage3.9 tons
- Round to4 tons
- Airflow at 400 CFM/ton1,560 CFM
- CautionConfirm with a Manual J before buying
Frequently asked questions
Is bigger safer?
No — an oversized system short cycles, leaves the house clammy and wears out faster.
Why does insulation matter so much?
A tight, well-insulated house can need 40% less capacity than an equal-sized leaky one.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.