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Pipe pressure drop calculator: friction loss with Darcy-Weisbach

Friction and minor losses of a pipe with Darcy-Weisbach and Colebrook-White, in kPa and metres of head, from flow rate or velocity. Free, no sign-up.

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  • Formula and standards shown
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Pre-filled example

100 m of steel pipe (roughness 0.045 mm), 50 mm inside diameter, carrying 10 m³/h of water at 20 °C, with fittings whose coefficients add up to 4.

mm
m³/h
m
mm
cSt
kg/m³

Result

45.3kPaPressure drop Δp

Head loss
4.63m
Mean velocity
1.415m/s
Reynolds number
70,454
Friction factor λ
0.02269
λ by Swamee-Jain
0.02285
Minor losses
4.00 kPa
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Pressure drop results kept with the piping change

Here, the calculator is free and the result is gone when you close the page. In Reglova, it is attached to the work order on the right machine: you find it again at the next breakdown, and on audit day.

The CMMS software comparison, our gaps included
  • Attached to the work order with its inputs: the server recalculates it, it stays verifiable.
  • On the technician's phone, even without a network.
  • In the machine's history, for the next breakdown.
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Reglova · Calculations · Work order WO-AT01-04219
Silent video, 33 s: from the work order for an oil leak on a shear cylinder, the tightening torque of an M12 bolt, then "Attach to the work order". A step to tighten it to 93.1 N·m lands in the checklist (step text from the French demo data). Watch the video

When to calculate a pipe pressure drop

  1. 01

    Check that a pump will overcome a new length of pipework.

  2. 02

    Compare two diameters before renewing a network.

  3. 03

    Explain a lower flow after fouling, which increases roughness.

Good to know

Between Re 2,300 and 4,000, the flow is transitional and λ uncertain: the calculator keeps the higher of the two values.

Darcy-Weisbach formula and Colebrook friction factor

The calculator gives a pipe's pressure drop in kPa and in metres of liquid column, with the Reynolds number and the Colebrook-White friction factor λ (and its Swamee-Jain value for comparison). Add the sum of the loss coefficients of bends, valves and tees to get the minor losses.

Formula · Reference documents

Δp = λ·(L/D)·ρ·v²/2 ; Re = v·D/ν ; laminar λ = 64/Re ; Colebrook 1/√λ = −2·log10(ε/3.7D + 2.51/(Re·√λ)) ; Swamee-Jain λ = 0.25/[log10(ε/3.7D + 5.74/Re^0.9)]²

Darcy-Weisbach ; Colebrook-White (1939) ; Swamee-Jain (1976)

Inputs and accepted ranges
InputUnitAccepted rangeExample
Inside diametermm1 to 3,00050 mm
Known value2 optionsFlow
Flowif Known value: Flowm³/h0.0001 to 100,00010 m³/h
Mean velocityif Known value: Velocitym/s0.0001 to 100
Pipe lengthm0.01 to 100,000100 m
Roughness εmm0 to 100.045 mm
Kinematic viscositycSt0.01 to 100,0001.004 cSt
Liquid densitykg/m³500 to 2,000998.2 kg/m³
Sum of minor loss coefficients Σζ0 to 1,0004
Calculated results
  • Pressure drop ΔpkPa
  • Head lossm
  • Mean velocitym/s
  • Reynolds number
  • Friction factor λ
  • λ by Swamee-Jain
  • Minor losseskPa
What the calculator flags
  • Flow in the transition zone (Re 2,300 to 4,000): the larger λ is used.

Network changes traced from request to restart

  • Breakdowns reported by QR code
  • Work orders on the phone, even without a network
  • Mandatory inspections reminded by email
  • Audit file as a PDF, in one click
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