Round to Rectangular Duct Conversion Table (Equivalent Diameter)

Convert round to rectangular, or rectangular to round, duct sizes for HVAC applications.
This chart is based on the “duct friction loss formula”; rectangular dimensions & airflow volume adapted to the equal friction loss method of sizing ventilation duct systems. Approx. friction loss of 0.8″ water gauge / 100 ft duct (6.6 Pa/m).
Bold: popular “standard” (available from Home Depot, Lowe’s, and other major hardware stores) rectangular duct sizes for conversion from Futuro Futuro standard 6″ round ducts.

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