AC Tonnage Calculator
Convert air conditioner capacity between tons, BTU/h and kW, read the tonnage hidden in an AC model number, or estimate tons from system airflow.
A refrigeration ton measures cooling output: 12,000 BTU per hour, approximately 3.516853 kW. This calculator converts output units, compares an illustrative list of nominal capacities, and shows what a verified model-number capacity code means. Airflow mode provides a rule-of-thumb comparison only; airflow by itself does not determine the cooling capacity of equipment.
How to use this tool
- Choose what you know: a load in BTU/h, a capacity in kW, the model number, or the airflow.
- Enter that value, or pick the size number you found in the model number.
- Read equivalent capacity units and the next capacity in the illustrative list.
- Use the table to compare listed nominal capacities and assumed airflow.
Formula
tons = BTU/h ÷ 12,000 = kW ÷ 3.5169 ≈ CFM ÷ 400
Tons = BTU/h ÷ 12,000. A capacity code such as 036 means 36,000 BTU/h only where the manufacturer defines it that way. Airflow mode assumes 400 CFM/ton and displays a 350–450 CFM/ton sensitivity band; these are illustrative ratios, not measured capacity or installation limits.
Example
A stated cooling output of 26,000 BTU/h converts to 2.17 tons or about 7.62 kW. The next capacity in this calculator’s list is 2.5 tons (30,000 BTU/h). At an assumed 400 CFM/ton that corresponds to 1,000 CFM. This comparison does not show that a nominal 2.5-ton product meets a building’s actual sensible and moisture requirements.
Frequently asked questions
Where is the tonnage in my model number?
Use the brand’s model-number documentation to identify the capacity field. The same digits can mean something else in a different model family. This calculator interprets a code already confirmed to represent thousands of BTU/h; it does not decode an arbitrary model number.
Is a 3-ton unit always 36,000 BTU/h?
36,000 BTU/h is the nominal arithmetic meaning of three tons. Rated and delivered capacity depend on the tested combination and operating conditions. Use the manufacturer’s expanded performance data for the matched indoor and outdoor equipment.
How many square feet does one ton cool?
There is no fixed floor area per ton. Envelope, windows, leakage, ventilation, design weather and internal gains matter. Use a qualified building-load calculation before selecting equipment rather than converting floor area directly.
How much electricity does a ton use?
Tons measure heat removal, not electrical input. If actual cooling output and EER2 refer to the same rating point, dividing BTU/h by EER2 gives watts: 36,000 ÷ 12 = 3,000 W. This is a rating-point illustration, not an annual energy forecast.
Sources
Last updated: 2026-10-30