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CFM per Ton Calculator

Required airflow from tonnage at 350–450 CFM/ton, tuned to your climate — and a quick check of measured airflow against the target band.

Rated by
tons

Humid climates run lower CFM/ton for more moisture removal.

CFM

Enter a metered CFM to check actual CFM/ton.

Required airflow
400 CFM/ton target
1,200CFM
Required CFM
1200
CFM/ton
400
Tons
3
ƒShow the math
  1. 1.Nominal tons

    Nameplate cooling tons.

    = 3 tons
  2. 2.Required airflowper industry nominal 350–450 CFM/ton
    CFM = tons × target CFM/ton
    3 × 400
    = 1200 CFM
Before you rely on this
  • Use 350–375 in humid climates for more moisture removal, 400 at rating conditions, and up to 450 in dry climates or heat-pump heating.

Why 400 CFM per ton

A ton of cooling is 12,000 BTU/h. Manufacturers rate equipment at roughly 400 CFM per ton because that airflow splits the coil’s capacity into a sensible-heavy mix that suits most comfort-cooling jobs.

  • 350–375 CFM/ton — humid climates. Colder coil, more moisture pulled out.
  • 400 CFM/ton — the rating default and a safe starting point.
  • 450 CFM/ton — dry climates and heat-pump heating, where dehumidification matters less.

Getting that airflow through the duct is a separate question — the blower has to overcome the system’s static pressure. Confirm the number in the field rather than assuming nameplate CFM.

Frequently asked

How many CFM per ton for an AC?
About 400 CFM per ton at rating conditions, and a working range of 350 to 450. Use 350–375 in humid climates for more dehumidification, 400 as the default, and up to 450 in dry climates or when a heat pump is in heating. A 3-ton system at 400 CFM/ton needs 1,200 CFM.
How do I convert tons to CFM?
Multiply tons by your target CFM/ton. Required CFM = tons × CFM/ton. For 3 tons at 400, that is 1,200 CFM. If you only have BTU/h, divide by 12,000 to get tons first — 36,000 BTU/h is 3 tons.
What happens with too little airflow?
Below about 350 CFM/ton the coil runs colder: you get more moisture removal but risk freezing the coil, low capacity, and possible liquid floodback. It usually traces to a dirty filter or coil, undersized or restricted duct, or a blower set too slow.
What happens with too much airflow?
Above about 450 CFM/ton the coil runs warmer, so it dehumidifies poorly and the temperature split narrows. Rooms can feel cool but clammy. Turning the blower speed down restores dehumidification, especially in humid weather.
How do I measure actual CFM per ton?
Divide measured airflow by tonnage. Get airflow from a TrueFlow grid, a flow hood totaled at the registers, or the temperature-rise method on the furnace, then divide by tons. Enter it here to see whether you are inside the 350–450 band.

Related tools

HVAC
Static Pressure Calculator

Check whether the blower can actually move this airflow.

HVAC
Target ΔT Calculator

A wide split is often the low-airflow symptom.

HVAC
Duct Size Calculator

Size the duct to carry the required CFM.

Sources & references

Estimates for planning purposes only. Verify all results against the code edition adopted in your jurisdiction and with your Authority Having Jurisdiction (AHJ). This tool is not a substitute for a licensed HVAC contractor. See our methodology, sources, and code editions.