Duct Size Calculator
Get the round duct diameter and the equivalent rectangular duct size for a given airflow and velocity — the quick check every HVAC layout needs. Adjust the inputs, then get an engineered ductwork design.
Your airflow
Sizes ducts on the velocity method (area = airflow ÷ velocity). A full design also balances friction loss, noise (NC) and the static pressure across the run.
Get an engineered ductwork design — free
Our HVAC engineers will size the full duct network, diffusers and static pressure for your project. We'll attach the estimate above automatically.
Your request is in
Thanks! Our HVAC team will send your tailored ductwork design within one business day.
Indicative estimates only — not a binding design. Actual ducting depends on the friction rate, aspect ratio, fittings, noise criteria and available ceiling space.