FreeHVACCalculators

CFM per Ton Calculator

Check whether a system moves the right amount of air for its size, or find the blower airflow to aim for.

Method reviewed October 22, 2026. Version 1.0.0. How it works

Your inputs

Unit system

Result

Airflow per ton
400CFM/ton

400 CFM/ton is within the typical 350–450 range.

Difference from 400 CFM/ton
0%
Show the working
  1. CFM per ton = airflow ÷ tons
    1,200 / 3 = 400 CFM/ton

Why 400 is only the starting point

“400 CFM per ton” is the nominal design value, but the right airflow depends on climate. Lower airflow, around 350 CFM per ton, keeps the coil colder and removes more moisture — useful in humid regions. Higher airflow, around 450, favours sensible capacity in dry climates. ACCA and other building-science sources describe this range and recommend following the manufacturer’s airflow tables for the specific equipment.

What a reading outside the range suggests

  • Below about 300 CFM per ton: risk of a frozen coil and lost capacity. Check filter, coil, blower speed and restrictive ducts.
  • Above about 450: less dehumidification and more noise; sometimes a blower set to a heating speed in cooling mode.

Airflow must be measured, not guessed. Common methods are a flow hood at the registers, a duct traverse, or static pressure read against the blower’s fan table.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

I want to
Check CFM per ton from measured airflow
Measured airflow
1,200 CFM
Nominal cooling capacity
3 tons

Result

Airflow per ton
400 CFM/ton
Difference from 400 CFM/ton
0 %

400 CFM/ton is within the typical 350–450 range.

Assumptions

  • Uses nominal tonnage (12,000 BTU/h per ton). Actual delivered capacity varies with conditions.

Limitations

  • Measured airflow needs a reliable method (e.g. traverse, flow hood or static-pressure/fan-table method). Always follow the equipment manufacturer’s airflow specification.

Frequently asked questions

How many CFM is a 3-ton unit?

About 1,200 CFM at 400 CFM per ton, or 1,050–1,350 CFM across the typical 350–450 range. The equipment’s installation manual lists the allowed range.

Does CFM per ton apply to heat pumps in heating mode?

Heat pumps also use roughly 350–450 CFM per ton in heating, but manufacturers specify the airflow for each mode and stage. Furnaces are set by temperature rise instead.

Sources

  1. 400 CFM per Ton, or Is It? — ACCA HVAC Blog (M. Akins). 400 CFM/ton is a rule of thumb; about 350 suits humid climates and about 450 drier climates; follow OEM airflow tables.
  2. Getting the Right Airflow for an Air Conditioning System — Green Building Advisor (A. Bailes). 300–350 CFM/ton for humid climates, 400 nominal, 450–550 for dry climates.

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