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)
26.6 mm
Pass

Minimum actual ID for the entered velocity target.

Also computed

Flow area (A) 555.6 mm²

Pressure drop (dp) 0.3244 bar

f = 0.0221, turbulent flow

Head loss (h) 3.315 m

Pipe velocity (v) Pass 1.5 m/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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