Duct Velocity

Calculate velocities in circular and rectangular ducts - imperial and SI-units - online calculator

Imperial Units

The velocity of air in a ventilation duct can be expressed in imperial units like

v_i = q_i / A_i = 576 q_i / (π d_i²) = 144 q_i / (a_i b_i)         (1)

where

v_i = air velocity (ft/min)

q_i = air flow (cfm)

A_i = area of duct (square feet)

d_i = diameter of duct (inches)

a_i = width of duct (inches)

b_i = width of duct (inches)

Imperial Units Air Flow Velocity Calculator

Air velocity can be calculated with the calculator below. Add air volume - q - and diameter - d - (or length a and b).

Air volume - q_i - (cfm)

Diameter - d_i - (inches)

or alternatively

Length side - a_i - (inches)

Length side - b_i - (inches)

SI - Units

Air velocity in a duct can alternatively be expressed in SI units like

v_m = q_m / A_m = 4 q_m / (π d_m²) = q_m / (a_m b_m)         (2)

where

v_m = air velocity (m/s)

q_m = air flow (m³/s)

A_m = area of duct (m²)

d_m = diameter of duct (m)

a_m = width of duct (m)

b_m = width of duct (m)

SI Units Air Flow Velocity Calculator

Air velocity can be calculated with the calculator below. Add air volume - q - and diameter - d - (or length a and b).

Air volume - q_m - (m³/s)

Diameter - d_m - (m)

or alternatively

Length side - a_m - (m)

Length side - b_m - (m)

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