Pipe Flow Pressure Drop Calculator

Estimate water-pipe velocity, Reynolds number, Darcy friction factor, pressure drop, head loss and pump power loss from flow, pipe ID, length, fluid properties and fittings.

Inputs

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Flow rate (Q)

Volumetric flow through the pipe.

L/min

Pipe inside diameter (D)

Actual inside diameter, not nominal pipe size.

Pipe length (L)

Straight equivalent pipe length.

Fluid density (rho)

Water is about 998 kg/m^3 near room temperature.

kg/m³

Dynamic viscosity (mu)

Water is about 1 cP near room temperature. Glycol mixes can be much higher.

Roughness (epsilon)

Equivalent internal roughness. Smooth plastic/copper is low; rough steel is higher.

Fitting loss coefficient (sum K)

Sum of minor-loss K values for elbows, tees, valves and fittings.

Results

Default result

Edit inputs

Pressure drop(dp)

0.4334bar

f = 0.0218, turbulent flow

Also computed

Head loss(h)4.429m

Pipe velocity(v)1.698m/s

Reynolds number(Re)42,360

turbulent

Darcy friction factor(f)0.02178

Hydraulic power loss(P_loss)0.03612kW

Method notes 3 notes

Darcy-Weisbach: dp = (f*L/D + sum K) * rho*v^2/2. Laminar f = 64/Re; turbulent f uses Swamee-Jain.
Use actual pipe ID and fluid viscosity at operating temperature. Nominal pipe size alone is not enough.
This is a piping screen only. Final plumbing, hydronic or process designs still need adopted code, manufacturer data, pump curves, valves, strainers, water hammer, erosion/corrosion and balancing checks.

Pipe pressure drop follows Darcy-Weisbach: dp = (f*L/D + sumK)*rho*v^2/2. Flow and actual pipe ID set velocity, viscosity sets Reynolds number and friction factor, and fittings add minor losses through K values. This calculator returns pipe velocity, Reynolds number, pressure drop, head loss and hydraulic power loss for water-like piping screens.

How to use this calculator

Enter flow and pipe ID. Use actual inside diameter and the design flow rate.
Enter length and fittings. Use straight pipe length plus a fitting K allowance.
Set fluid properties. Use density and viscosity at operating temperature.
Check velocity and loss. Compare velocity, head loss and pressure drop with the system target.

How it works

Flow and pipe inside diameter set velocity:

v = Q / A

Reynolds number sets the friction-factor method:

Re = rho x v x D / mu

Pressure drop uses Darcy-Weisbach plus fitting losses:

dp = (f x L/D + sumK) x rho x v^2 / 2

Head loss converts pressure drop back into equivalent fluid column height:

head = dp / (rho x g)

Worked example

Verified against the live calculator

For 50 L/min through a 25 mm ID pipe over 30 m, water velocity is about 1.7 m/s. With a small roughness and sumK = 4, the calculator reports the Darcy pressure drop and equivalent head loss for an early pump/system screen.

Frequently asked questions

How do you calculate pipe pressure drop?

The calculator uses Darcy-Weisbach: pressure drop equals friction and fitting losses times dynamic pressure. Flow and pipe ID set velocity, viscosity sets Reynolds number and friction factor, and fittings add minor-loss K values.

Is this for plumbing or hydraulic hose?

This page is aimed at water-like pipe systems: plumbing, hydronic, process and shop piping screens. Hydraulic oil hoses should use the hydraulic hose pressure drop calculator because oil viscosity and hose velocity limits differ.

Why does actual pipe ID matter?

Pressure drop changes strongly with diameter. Nominal pipe size is not enough because schedule, material and fittings change the real inside diameter.

Does this size a pump?

No. It reports pipe pressure drop, head loss and hydraulic power loss. Final pump selection needs a pump curve, system curve, valves, strainers, elevation, NPSH and control requirements.

Method & assumptions

Uses Darcy-Weisbach with laminar f = 64/Re and Swamee-Jain turbulent friction.
Requires actual pipe inside diameter and fluid viscosity at operating temperature.
Does not model pump curves, elevation, NPSH, water hammer, pipe aging, valve position, strainers, heat exchange, erosion/corrosion or code requirements.
Use hydraulic hose pressure drop, pump flow and HP and steel pipe schedule for adjacent sizing checks.

Pipe Flow Pressure Drop Calculator

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