Duct Velocity

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

The velocity in ventilation ducts can be calculated in imperial or SI units.

air duct

Duct Velocity in Imperial Units

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

vi = qi / Ai

    = 576 qi / (π di2)

    = 144 qi / (ai bi)         (1)

where

vi = air velocity (ft/min)

qi = air flow (cfm)

Ai = area of duct (square feet)

di = diameter of duct (inches)

ai = width of duct (inches)

bi = width of duct (inches)

Example - Air Flow Velocity in a Duct

The velocity in a 12 inch duct with air flow 1000 cfm can be calculated as

vi = 576 (1000 cfm) / (π (12 in)2)

   = 1273 (ft/min)

Air Flow Velocity Calculator - Imperial Units

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

Air volume - qi - (cfm)

Diameter - di - (inches)

or alternatively

Length side - ai - (inches)

Length side - bi - (inches)

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Duct Velocity in SI - Units

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

vm = qm / Am

     = 4 qm / (π dm2)

     = qm / (am bm)         (2)

where

vm = air velocity (m/s)

qm = air flow (m3/s)

Am = area of duct (m2)

dm = diameter of duct (m)

am = width of duct (m)

bm = width of duct (m)

Example - Air Flow Velocity in a Duct

The velocity in a rectangular 0.5 m x 0.5 m duct with air flow 1 m3/s can be calculated as

vm = (1 m3/s) / ((0.5 m) (0.5 m))

   = 4 (m/s)

Air Flow Velocity Calculator - SI Units

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

Air volume - qm - (m3/s)

Diameter - dm - (m)

or alternatively

Length side - am - (m)

Length side - bm - (m)

Related Topics

  • Ventilation - Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more

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