How many CFM per ton does an AC system need?

The standard is 400 CFM/ton. High efficiency or variable speed equipment typically runs 350–375 CFM/ton, and high sensible heat applications 425–450 CFM/ton. Always verify against manufacturer specifications.

How much is one ton of cooling?

One ton of cooling capacity equals 12,000 BTU/hr. A 3-ton system at 400 CFM/ton requires 1,200 CFM of total airflow.

Tonnage to CFM Calculator

Convert AC tonnage to the expected airflow in CFM using the standard rule of thumb.

Calculator

Equipment Capacity (tons)

Airflow Rate (CFM per ton)

Required airflow

0 CFM

Enter values above and click calculate.

How It Works

This calculator converts AC equipment tonnage to an estimated airflow requirement using the standard industry rule of thumb. It's commonly used when sizing ductwork, checking system balance, or estimating airflow for equipment selection.

CFM = Tons x 400

Metric: L/s = kW x 53.7

Where:
Tons = cooling capacity of the equipment — 1 ton equals 12,000 BTU/hr
CFM/ton = airflow rate per ton of cooling — the standard is 400 CFM/ton but this varies by equipment and application
CFM = total required airflow in cubic feet per minute

Typical CFM/ton values:
Standard residential systems: 400 CFM/ton
High efficiency or variable speed: 350–375 CFM/ton
High sensible heat applications: 425–450 CFM/ton

Common Example: A 3-ton system at 400 CFM/ton requires 1,200 CFM of total airflow.

In metric, capacity is in kW of cooling (1 ton = 3.517 kW) and airflow in litres per second. 400 CFM/ton works out to about 53.7 L/s per kW, so a 10.5 kW system needs about 564 L/s.