CFM per ton, from cooling capacity.

Short answer

System airflow = tons of cooling x CFM per ton, and one ton is 12,000 Btu/h. A 3 ton (36,000 Btu/h) system at 400 CFM per ton moves 1200 CFM, and the typical 350 to 450 range is 1050 to 1350 CFM. A measured 1,100 CFM on that system is 367 CFM per ton.

Worked example

A 36,000 Btu/h air conditioner is 36,000 / 12,000 = 3 tons. At 400 CFM per ton that is 1200 CFM, within a 1050 to 1350 CFM range. If a technician measures 1,100 CFM across the system, that is 1,100 / 3 = 367 CFM per ton.

Formula, assumptions and sources

A Florida Solar Energy Center paper presented at the 1997 ASHRAE Annual Meeting states that typical target airflow rates are approximately 350 to 450 cubic feet per minute per ton, and that about 425 to 450 CFM per ton through a dry coil is usually needed to reach 400 CFM per ton across a wet coil. This tool applies those figures as a typical range, not a requirement. The ton is the refrigeration ton, 12,000 Btu per hour (International Table Btu), as listed in NIST's SI conversion guide. The right airflow for a given system is set by the manufacturer's installation data and the application, including humidity control; the range is not a substitute for it, and airflow should be measured rather than assumed.

Source: Florida Solar Energy Center, Impact of Evaporator Coil Air Flow in Residential Air Conditioning Systems (1997 ASHRAE Annual Meeting) (retrieved 2026-10-15)

Source: NIST Guide to the SI, Appendix B.8: ton of refrigeration (retrieved 2026-10-15)

Safety and limits

This is a planning aid, not professional advice. Duct, furnace and air-conditioner design affects comfort, combustion safety and code compliance; a licensed HVAC contractor should perform a load calculation, size the system and verify airflow on site.

FAQ

How many CFM per ton of air conditioning?

The typical target for residential split systems is about 350 to 450 CFM per ton, with 400 CFM per ton the common reference point. Check the equipment manufacturer's data for your unit.

How many Btu/h is one ton?

One ton of cooling is 12,000 Btu per hour, which NIST lists as 3,516.85 watts.

Should I use 350 or 450 CFM per ton?

It depends on the equipment, the climate and how much humidity control you want. The manufacturer's installation instructions decide; this tool only shows the range.

How do I find the CFM per ton of my system?

Have a technician measure the airflow, then divide it by the system's capacity in tons. Enter the measured CFM here to see the result.