Duct Sizing Calculator
Size a duct run by the equal-friction method: enter the airflow and the friction rate you are designing to, and get the round diameter, the equivalent rectangular sizes, the resulting velocity and the velocity pressure for each run.
Velocity matters as much as size. A duct that meets the friction target but runs too fast becomes an occupant complaint that no balancing damper will fix, so the velocity for each run is shown alongside the size rather than buried in a schedule.
Need the whole set drawn and stamped? Ask for a fixed quote, or see the other calculators.
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