Ductsize                                     Air temperature   20C   50% RH

Volume flow  


Circular    diameter mm   

Flat oval mm (width) x mm (height)

Rectangular  mm (width) x mm (height)

Velocity  m/s  (typical 2 to 10 m/s)


Material    Roughness  k  mm              See CIBSE C guide table 4.1  



Pressure drop per unit length   Pa / m   (typical 1 Pa/m for low vel) Effective diameter   mm 
Velocity Pressure Pa Reynolds Number  
Equivalent length le  (length for pressure drop of 1 velocity pressure)