Air Flow (CFM) Calculator
Calculate the airflow (CFM) needed to carry a sensible cooling load over a temperature difference.
Estimates for planning only — verify against local HVAC codes and a qualified engineer.
How it works
- 1Enter the sensible cooling load in kilowatts (kW).
- 2Enter the temperature difference between supply air and the room (ΔT).
- 3The calculator applies Q = load ÷ (ρ·cp·ΔT) and converts to CFM, m³/s, m³/h, and L/s.
Use cases
- Sizing supply diffusers and ductwork for HVAC systems.
- Verifying a fan or air-handling unit delivers enough airflow.
- Energy-audit checks that airflow matches the cooling capacity.
Frequently asked questions
What formula does the calculator use?
Q = load ÷ (ρ·cp·ΔT), with ρ = 1.225 kg/m³ and cp = 1005 J/kg·K. 3.5 kW over 8 °C gives ≈ 0.357 m³/s ≈ 757 CFM.
Why does a bigger ΔT need less airflow?
Each cubic metre of supply air carries more heat at a larger temperature difference, so fewer m³/s are needed for the same total load.
CFM or m³/s — which should I use?
CFM is standard on North American equipment; m³/s or L/s is used in metric design documents. The tool shows both.
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