Pipe Size by Flow Velocity Calculator

Inputs

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Volumetric flow through the pipe.
L/min
Velocity target used to back-solve pipe inside diameter.
m/s
Straight equivalent pipe length used for pressure-drop screening.
m
Water is about 998 kg/m^3 near room temperature.
kg/m³
Water is about 1 cP near room temperature. Glycol mixes can be much higher.
cP
Equivalent internal roughness. Smooth plastic/copper is low; rough steel is higher.
mm
Sum of minor-loss K values for elbows, tees, valves and fittings.

Results

Default result
Edit inputs
Required pipe ID(D)
26.6mm
Pass

Minimum actual ID for the entered velocity target.

Also computed

Flow area(A)555.6mm²

Pressure drop(dp)0.3244bar

f = 0.0221, turbulent flow

Head loss(h)3.315m

Pipe velocity(v)Pass1.5m/s

Reynolds number(Re)39,810

turbulent

Darcy friction factor(f)0.02207

Method notes 3 notes
  • Required area = Q / v, and required ID = sqrt(4A/pi). Pressure loss uses the same Darcy-Weisbach model as the pipe pressure-drop calculator.
  • Select a nominal pipe whose actual inside diameter is at least this result, then re-check pressure drop with the actual pipe ID.
  • Final plumbing, hydronic and process designs still need code requirements, pump curves, pipe schedule, fittings, valves, water hammer, erosion/corrosion and balancing checks.

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