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# Duct Velocity

## Calculate velocities in circular and rectangular ducts - imperial and SI-units - online calculator. ### Air Duct Velocity - Imperial Units

Air velocity in a ventilation duct can be calculated in imperial units as

v i = q i / A i

= q i / [ π (d f / 2) 2 )]

= q i / [ π ((d i / 12) / 2) 2 )]

= (576 / π) ( q i / d i 2 )

= 144 q i / (a i b i )                                   (1)

where

v i = air velocity (ft/min)

q i = air flow (ft 3 /min)

A i = area of duct (ft 2 )

d f = diameter of duct (ft)

d i = diameter of duct (in)

a i = width of duct (in)

b i = width of duct (in)

#### Example - Air Flow Velocity in a Duct

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

v i = (576 / π )  (1000 cfm) / (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 ).

or alternatively

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### Air Duct Velocity - SI Units

Air velocity in a duct can be calculated in SI units

v m = q m / A m

= q m / (π (d m / 2) 2 )

= 4 q m / (π d m 2 )

= q m / (a m b m )                                  (2)

where

v m = air velocity (m/s)

q m = air flow (m 3 /s)

A m = area of duct (m 2 )

d m = diameter of duct (m)

a m = width of duct (m)

b m = 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 m 3 /s can be calculated as

v m = (1 m 3 /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 ).

or alternatively

### Air Ducts - Velocity Diagram

The chart below can be used to estimate velocities in air ducts.

The default values are for air flow 400 cfm (680 m 3 /h) , duct size 8 in (200 mm) and velocity 1150 fpm (5.8 m/s) . Air Ducts Friction Loss ## Related Topics

• ### Ventilation

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

## Related Documents

• ### Air Duct Velocities

Typical air duct velocities in applications like ventilation systems or compressed air systems.
• ### Air Ducts - Friction Loss Diagram

A major friction loss diagram for air ducts - Imperial units ranging 10 - 100 000 cfm.
• ### Air Ducts - Friction Loss Diagram

A major friction loss diagram for air ducts - SI units.
• ### Air Ducts - Major Friction Head Loss, Online Calculator

Head loss or major loss in air ducts - equations and online calculator for rectangular and circular ducts - Imperial and SI units.
• ### Air Ducts - Sizing

Required duct area vs. air flow.
• ### Air Ducts - Velocity Diagram

Air flow volume, duct size, velocity and dynamic pressure.
• ### Circular Ducts - Dimensions

Standard size of circular ventilation air ducts.
• ### Colebrook Equation

Friction loss coefficients in pipes, tubes and ducts.
• ### Duct Sizing - the Equal Friction Method

The equal friction method for sizing air ducts is easy and straightforward to use.
• ### Ducts - Cross-Sectional Area vs. Diameter

Circular ducts sross-sectional areas.
• ### Ducts - Sheet Metal Gauges

Thickness of sheet metal used in ductwork.
• ### Ducts or Pipes through Steel Joists - Maximum Sizes

Maximum sizes of ducts or pipes through K series joists.
• ### Ducts Sizing - the Velocity Reduction Method

The velocity reduction method can be used when sizing air ducts.
• ### Ductwork - Seal Classes

Ductwork air leakage classes.
• ### Exhaust Outlets - Capturing Air Velocities

Capturing air velocity in front of an exhaust outlet - online exhaust outlet velocity calculator.
• ### Fluid Flow - Hydraulic Diameter

Calculate hydraulic diameter for pipes and ducts.
• ### HVAC Ducts - Air Velocities

Recommended air velocities in HVAC ducts.
• ### Sizing Circular Ducts

A rough guide to maximum air volume capacity of circular ducts in comfort, industrial and high speed ventilation systems.
• ### Spiral Ducts - Dimensions

Standard dimensions of spiral ducts - Imperial units.
• ### Velocity Classification of Ventilation Ducts

Recommended air velocities in ventilation ducts
• ### Velocity Units Converter

Convert between speed and velocity units like m/s, km/h, knots, mph and ft/s.

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## Citation

• The Engineering ToolBox (2005). Duct Velocity. [online] Available at: https://www.engineeringtoolbox.com/ductwork-equations-d_883.html [Accessed Day Month Year].

Modify the access date according your visit.

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