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Sewer Pipes - Capacities vs. Slope

Carrying capacities of sewer and wastewater pipes - gpm and liter per second.

The diagrams below can be used for design of sewage and wastewater gravity conveying systems.

Sewage Pipe Capacity - Imperial units - gpm

Sewage wastewater pipe - capacity in gpm

Sewage Pipe Capacity - SI Units - liter per second

Sewage wastewater pipe - capacity in liter per second

Note! - the charts are based on clean plastic pipes - calculated with the Manning formularoughness coefficient 0.015 and fill 50%.

@Example - Capacity of a Sewer Pipe

The capacity of a 4 inch sewer pipe with decline 0.5% is aprox. 25 gpm (1.6 liter/s).

  • 1 gal (US)/min = 6.30888x10-5 m3/s = 0.227 m3/h = 0.06309 dm3(liter)/s = 2.228x10-3 ft3/s = 0.1337 ft3/min = 0.8327 Imperial gal (UK)/min

Decline and Slope

Calculate between decline and slope units

d = 8.33 s(in/ft)

   = 100 s(ft/ft)

   = 100 s(m/m)

   = s(ft/100ft)                                                    (1)


d = decline (%)

s = slope

Example - % Decline

1/8 in/ft slope can be transformed to % decline as

d = 8.33 (1/8 in/ft)

   = 1.04 %

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