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Pressure drop in pipe calculator

Related calculators: Pipe diameter; Reynolds number

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Pressure drop in pipe calculator can be used for pressure drop and flow rate calculation for all Newtonian fluids with constant density in closed round or rectangle pipe. You can calculate pressure drop or flow rate through a pipe including friction coefficient - f calculation.

Pressure drop is calculated for known flow rate, pipe diameter, pipe length, fluid density and viscosity. For flow rate calculation, pressure on the start and on the end of pipe is required, as well as pipe diameter, pipe length, fluid density and viscosity.

Pressure drop in pipe calculation is based on the Darcy-Weisbach equation for head loss due to friction in closed round or rectangle pipe. Local resistances factor K for valves, fittings, pipes contraction and enlargement should be entered in calculator.

Values of local resistances for some fittings (tees, elbows, reducers) can be found in calculator itself, or you can calculate it with  resistance coefficient calculator.

Calculation due to friction is based on the Darcy equation.

Pressure difference in pipe due to change of height is not included in this version of calculator, but you can still calculate flow rate if available head of fluid height is entered as pressure difference.

Pressure drop calculator can be used for both laminar and turbulent flow regime, as Reynolds number of flow is calculated and presented in results. Reynolds number itself you can calculate with Reynolds number calculator.

For compressible flow pressure drop calculation you can use gas flow calculator.

For turbulent flow (Re > 4000) friction factor is calculated using on the Colbrook and White equation (1937).

In rectangle pipes, instead of pipe diameter, hydraulic diameter is used.


  • Δ p - pressure drop
  • Q - volumetric flow rate
  • L - pipe length
  • v - velocity
  • f - friction coefficient
  • e - pipe roughness
  • K - minor losses coefficient
  • ρ - fluid density
  • Re - Reynolds number
  • D - pipe diameter
  • Dh- hydraulic diameter
  • a - channel height of rectangle pipe
  • b - channel width of rectangle pipe
  • A - cross section area
  • O - wetted perimeter

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