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Pipe size & pressure drop
Enter the flow, the bore and the run. The calculator returns velocity, flow regime, friction factor and the pressure drop — including an allowance for the fittings, which usually matter more than the straight pipe.
Your figures
The inside diameter, not the nominal size — schedule changes it.
Bends, valves and tees as equivalent straight pipe. 20–50% is usual.
Water 1, milk 2, vegetable oil 40–70 at working temperature, molasses 5,000+.
Result
Flow condition
- Velocity
- 1.77 m/s
- Reynolds number
- 176,839
- Friction factor
- 0.019
Normal for a pumped liquid line
Turbulent flow
Darcy–Weisbach
Pressure loss
- Pressure drop
- 0.384 bar
- Head loss
- 3.92 m
- Per 100 m
- 0.295 bar
- Equivalent length
- 130 m
Over 130 m equivalent length
Add this to the static lift when sizing the pump
For comparing routes
100 m straight + 30% for fittings
Questions
What velocity should I aim for?
Between about one and two and a half metres a second for a pumped liquid line. Slower and the pipe is larger and dearer than it needs to be, and solids settle out. Faster and you pay for the pressure drop every hour the pump runs, and erosion becomes a concern on anything abrasive.
Why an allowance for fittings?
Because bends, valves and tees often contribute more loss than the straight pipe between them, especially on a short congested run. Twenty to fifty percent of the straight length as equivalent pipe is the usual estimating allowance; a detailed design counts each fitting separately.
Which friction factor is used?
Laminar below Reynolds 2,300 is exact at 64 over Re. Above it the Swamee-Jain explicit fit to the Colebrook equation is used, at 0.045 mm roughness for commercial steel — within about one percent across the range this work happens in.
Is this the bore or the nominal size?
The internal bore. Nominal pipe size is not the inside diameter, and the schedule changes it — NB 100 schedule 40 is 102.3 mm inside, schedule 80 is 97.2 mm. Use the real figure from the pipe you are buying.