Equal Friction Method:
Using a predefined static pressure loss per unit of duct length, this online ductulator (Duct Size Calculator) calculates the diameter of round duct and the other dimension of rectangular duct. Based on the calculated dimensions, the air velocity will be calculated for both duct shapes and dimensions.

Velocity Method:
Using a predefined air velocity, this online Ductulator (Duct Size Calculator) calculates the diameter of round duct and the other dimension of a rectangular duct. Based on the calculated dimensions, the static pressure loss will be calculated for both duct shapes and dimensions. Note that unlike conventional ductulators, this ductulator will calculate the dimensions of the rectangular duct based on the given velocity and it then calculates the static pressure loss for the rectangular duct based on the given velocity and dimensions. Most old calculators will only use the given velocity to calculate the diameter of the round duct then it calculates the static pressure loss for the round duct and uses that static pressure to calculate the rectangular duct dimensions which is not the case here for more precise velocity output.

Dimensions Method:
Using a predefined duct dimensions, this online Ductulator (Duct Size Calculator) calculates the static pressure drop and air velocity of round duct and rectangular duct.

Colebrook equation is used to solve for Darcy's friction factor and calculates the static pressure loss in the duct until it matches the desired input at defined airflow and absolute roughness of the inner material of the duct touching the moving air.
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