Mechanical

Pipe Pressure Drop Calculator

Calculate indicative pipe pressure drop, velocity and head loss from flow rate, selected pipe size and equivalent length.

Use this calculator for preliminary closed water system checks where design flow rate, selected pipe size and equivalent pipe length are known. Based on a Darcy-Weisbach style pressure loss calculation using typical water properties and pragmatic pipe roughness assumptions.

Inputs

Equivalent pipe length should include allowances for valves, fittings and accessories where appropriate.

Result

Pressure Drop
-
Enter values and click calculate.

Method

Pipe velocity is calculated from flow rate and internal pipe area:

v = Q ÷ A

Internal pipe area is determined from:

A = πd² ÷ 4

Pressure loss is then estimated using the Darcy-Weisbach relationship:

ΔP = f × (L ÷ D) × (ρv² ÷ 2)
  • v = water velocity in pipe (m/s)
  • Q = volumetric flow rate (m³/s)
  • A = internal pipe area (m²)
  • f = Darcy friction factor
  • L = equivalent pipe length (m)
  • D = internal pipe diameter (m)
  • ρ = fluid density (kg/m³)
  • Calculated result = -

Reference

  • Pressure drop is estimated using a Darcy-Weisbach style approach with typical roughness values for copper and steel pipework.
  • Water density and viscosity are estimated from input water temperature for preliminary design purposes.
  • Relevant guidance may include CIBSE Guide B and CIBSE Guide C for heating system design, hydraulic distribution and pressure loss considerations.
  • Where applicable, final design should also align with relevant British Standards, project specifications and manufacturer requirements.
Design note: This calculator provides indicative straight-pipe pressure loss and equivalent-length based total loss only. Final hydraulic design should consider fittings, valves, coils, control valves, strainers, plate heat exchangers, glycol content, exact fluid properties and manufacturer data.

Related Calculators

Flow Rate Calculator Pipe Sizing Calculator Pump Head Calculator