Plumbing & Fluid

Pipe Pressure Drop Calculator

Solve full-pipe friction pressure loss, flow or inside diameter. Compare SI/US results and review the method, assumptions and related references below.

Change any input to update the calculation. Unit changes preserve the physical quantity.

CALCULATION SETUP

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YOUR CALCULATION

Results

Pressure drop

8.396 kPa1.2177 psi

Total loss head

0.8579 m2.8145 ft

Volume flow

2 L/s120 L/min7.2 m³/h31.7006 GPM (US)4.2378 CFM

Calculated / entered inside diameter

50 mm1.9685 in

Mean velocity

1.0186 m/s3.3418 ft/s

Reynolds number

50,726.6751

Darcy friction factor

0.0237

Straight-pipe head loss

0.7521 m2.4674 ft

Fitting head loss

0.1058 m0.3471 ft
Q 2 L/sv 1.019 m/sInside diameter 50 mm
Full circular pipe bore with flow and mean velocity · schematic, not to scale

Calculation breakdown

Pressure balance
Pipe friction + entered fitting K; static elevation and pump head excluded

Assumptions & checks

Friction and local losses only, not static elevation, terminal pressure, pump selection or open-channel drainage. Calculated inside diameter is not nominal pipe size.

KEEP THE JOB MOVING

Where does this result go next?

Input lookupWater Properties Table

Select documented fluid conditions

Previous stepPipe Diameter Calculator

Solve flow, velocity or bore

Input lookupPipe Fitting Loss Reference

Review bounded fitting scenarios

Next calculationPump TDH Calculator

Calculate total dynamic head

Follow the full workflow: Pipe sizing and flow check →Follow the full workflow: Pump system head and power check →

Formula

Solve full-pipe friction pressure loss, flow or inside diameter

Δp=ρg[(fL/D + ΣK)v²/(2g)]; v=4Q/(πD²); Re=vD/ν. f=64/Re for laminar flow, Colebrook for turbulent flow; transition uses an explicit interpolation. Worked example: 2 L/s through 50 mm bore has velocity 1.0186 m/s. Add length, roughness, viscosity and fitting K to calculate the loss, then reverse-solve the same pressure budget.

Worked example

Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.

Inputs

Volume flow
2 L/s
Actual inside diameter
50 mm
Straight pipe length
30 m
Absolute roughness
0.045 mm
Kinematic viscosity
1.004 cSt
Fluid density
998 kg/m³
Sum of fitting loss coefficients K
2

Result

Pressure drop
8.396 kPa
Total loss head
0.8579 m
Volume flow
2 L/s
Calculated / entered inside diameter
50 mm
Mean velocity
1.0186 m/s
Reynolds number
50,726.6751
Darcy friction factor
0.0237
Straight-pipe head loss
0.7521 m
Fitting head loss
0.1058 m

REAL INPUTS · CLEAR METHOD

Practical worked examples

Illustrative scenarios using this page’s calculation or verified reference model. Change the assumptions for your own job.

Water at 2 L/s through 30 m of 50 mm bore

Given

Volume flow
2 L/s
Actual inside diameter
50 mm
Straight pipe length
30 m
Absolute roughness
0.045 mm
Kinematic viscosity
1.004 cSt
Fluid density
998 kg/m³
Sum of fitting loss coefficients K
2
Calculation / lookup method

Δp=ρg[(fL/D + ΣK)v²/(2g)]; v=4Q/(πD²); Re=vD/ν. f=64/Re for laminar flow, Colebrook for turbulent flow; transition uses an explicit interpolation. Worked example: 2 L/s through 50 mm bore has velocity 1.0186 m/s. Add length, roughness, viscosity and fitting K to calculate the loss, then reverse-solve the same pressure budget.

Result

Pressure drop
8.396 kPa
Total loss head
0.8579 m
Volume flow
2 L/s
Calculated / entered inside diameter
50 mm
Mean velocity
1.0186 m/s
Reynolds number
50,726.6751

The total combines straight-pipe Darcy loss and entered fitting K. The fluid properties and roughness are explicit assumptions.

Laminar check: 10 mm bore at 0.1 m/s

Given

Volume flow
0.007853981633974483 L/s
Actual inside diameter
10 mm
Straight pipe length
10 m
Absolute roughness
0 mm
Kinematic viscosity
1 cSt
Fluid density
1000 kg/m³
Sum of fitting loss coefficients K
0
Calculation / lookup method

Δp=ρg[(fL/D + ΣK)v²/(2g)]; v=4Q/(πD²); Re=vD/ν. f=64/Re for laminar flow, Colebrook for turbulent flow; transition uses an explicit interpolation. Worked example: 2 L/s through 50 mm bore has velocity 1.0186 m/s. Add length, roughness, viscosity and fitting K to calculate the loss, then reverse-solve the same pressure budget.

Result

Pressure drop
0.32 kPa
Total loss head
0.0326 m
Volume flow
0.0079 L/s
Calculated / entered inside diameter
10 mm
Mean velocity
0.1 m/s
Reynolds number
1,000

Re = 1000 gives Darcy f = 64/Re and a 320 Pa pressure drop. This provides a transparent laminar benchmark of the unchanged solver.

Compare an 80 mm bore at the same 2 L/s

Given

Volume flow
2 L/s
Actual inside diameter
80 mm
Straight pipe length
30 m
Absolute roughness
0.045 mm
Kinematic viscosity
1.004 cSt
Fluid density
998 kg/m³
Sum of fitting loss coefficients K
2
Calculation / lookup method

Δp=ρg[(fL/D + ΣK)v²/(2g)]; v=4Q/(πD²); Re=vD/ν. f=64/Re for laminar flow, Colebrook for turbulent flow; transition uses an explicit interpolation. Worked example: 2 L/s through 50 mm bore has velocity 1.0186 m/s. Add length, roughness, viscosity and fitting K to calculate the loss, then reverse-solve the same pressure budget.

Result

Pressure drop
0.889 kPa
Total loss head
0.0908 m
Volume flow
2 L/s
Calculated / entered inside diameter
80 mm
Mean velocity
0.3979 m/s
Reynolds number
31,704.1719

Keeping flow, length, roughness and fittings fixed isolates the effect of bore. Larger bore reduces velocity and friction loss; it does not select a commercial pipe automatically.

Technical references for this calculation

Reference lookupCopper Tube Size Chart: K & LReference lookupCPVC CTS Pipe Size ChartReference lookupPipe Roughness ChartReference lookupPipe Size & Schedule Chart

Frequently asked questions

What does this result tell me?

Friction and local losses only, not static elevation, terminal pressure, pump selection or open-channel drainage. Calculated inside diameter is not nominal pipe size.

How can I check the calculation?

Worked example: 2 L/s through 50 mm bore has velocity 1.0186 m/s. Add length, roughness, viscosity and fitting K to calculate the loss, then reverse-solve the same pressure budget. Review each stated input and unit; use project-specific values rather than treating the editable example as a requirement.

Reference data & method sources

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