Pipe Pressure Drop Calculator

Q: Should I enter nominal size or internal diameter?

Enter the actual internal diameter. DN, NPS and outside diameter do not give the actual flow bore; obtain it from the pipe specification.

Q: Why does viscosity change the pressure loss?

Viscosity changes Reynolds number and the friction factor. Enter dynamic viscosity in mPa·s; do not enter kinematic viscosity in cSt directly.

Q: Can I select a pump from this result alone?

Also account for elevation, endpoint pressures, other equipment losses and the pump curve. This calculation gives the resistance loss of the entered pipe section.

Formula and method

v = 4Q/(πD²); Re = ρvD/μ; Δp = (fL/D + ΣK)ρv²/2; h = Δp/(ρg), with g = 9.80665 m/s². For Re ≤ 2000: f = 64/Re. For Re ≥ 4000: f = 0.25/[log₁₀(ε/(3.7D) + 5.74/Re⁰·⁹)]². The transition region uses EPA EPANET’s Dunlop cubic interpolation. Equations use SI units.

Worked example

Example: 10 m³/h, 50 mm bore, 20 m length, ε = 0.045 mm, ρ = 1000 kg/m³, μ = 1 mPa·s and ΣK = 2. Check velocity and flow regime before reviewing the losses.

Assumptions and limits

Flow must be positive; length, roughness and ΣK may be zero. The maximum accepted ε/D is 0.05.
Results for 2000 < Re < 4000 are transition-flow estimates. The Darcy factor is used; the Fanning factor is one quarter of it.
ΣK must reference the velocity at the entered bore. Defaults are demonstration values, with no automatic material or temperature selection; 1 mPa·s = 1 cP.
The result covers resistance losses only, excluding elevation, pump head, developing entrance flow, cavitation and transients. It does not model gases, two-phase flow or non-Newtonian fluids.

Frequently asked questions

Should I enter nominal size or internal diameter?

Enter the actual internal diameter. DN, NPS and outside diameter do not give the actual flow bore; obtain it from the pipe specification.

Why does viscosity change the pressure loss?

Viscosity changes Reynolds number and the friction factor. Enter dynamic viscosity in mPa·s; do not enter kinematic viscosity in cSt directly.

Can I select a pump from this result alone?

Also account for elevation, endpoint pressures, other equipment losses and the pump curve. This calculation gives the resistance loss of the entered pipe section.

References

Pipe Pressure Drop Calculator practical guide and common questions

What does Pipe Pressure Drop Calculator calculate?

For steady, fully developed flow of an incompressible Newtonian liquid in a full circular pipe of constant internal diameter. Enter the actual bore and fluid properties at operating temperature. v = 4Q/(πD²); Re = ρvD/μ; Δp = (fL/D + ΣK)ρv²/2; h = Δp/(ρg), with g = 9.80665 m/s². For Re ≤ 2000: f = 64/Re. For Re ≥ 4000: f = 0.25/[log₁₀(ε/(3.7D) + 5.74/Re⁰·⁹)]². The transition region uses EPA EPANET’s Dunlop cubic interpolation. Equations use SI units.

When is this useful?

Example: 10 m³/h, 50 mm bore, 20 m length, ε = 0.045 mm, ρ = 1000 kg/m³, μ = 1 mPa·s and ΣK = 2. Check velocity and flow regime before reviewing the losses.

How do I enter the inputs?

Enter the inputs for Pipe Pressure Drop Calculator: Actual volumetric flow, Flow unit, Actual internal diameter, Straight pipe length, Absolute roughness ε, Liquid density ρ, Dynamic viscosity μ, Sum of minor-loss coefficients ΣK. Calculate, check the units and assumptions, then copy or download the results.

How should I interpret the results?

Flow must be positive; length, roughness and ΣK may be zero. The maximum accepted ε/D is 0.05. Results for 2000 < Re < 4000 are transition-flow estimates. The Darcy factor is used; the Fanning factor is one quarter of it. ΣK must reference the velocity at the entered bore. Defaults are demonstration values, with no automatic material or temperature selection; 1 mPa·s = 1 cP. The result covers resistance losses only, excluding elevation, pump head, developing entrance flow, cavitation and transients. It does not model gases, two-phase flow or non-Newtonian fluids.

Where are my inputs processed?

Pipe Pressure Drop Calculator runs in this browser. Inputs are not uploaded to a calculation server; copying and CSV download require your action. The existing site analytics and advertising still load.