Pipe Size by Flow Velocity Calculator

Inputs

Flow rate (Q)

Volumetric flow through the pipe.

L/min

Target velocity (v)

Velocity target used to back-solve pipe inside diameter.

m/s

Pipe length (L)

Straight equivalent pipe length used for pressure-drop screening.

Fluid density (rho)

Water is about 998 kg/m^3 near room temperature.

kg/m³

Dynamic viscosity (mu)

Water is about 1 cP near room temperature. Glycol mixes can be much higher.

Roughness (epsilon)

Equivalent internal roughness. Smooth plastic/copper is low; rough steel is higher.

Fitting loss coefficient (sum K)

Sum of minor-loss K values for elbows, tees, valves and fittings.

Default result

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)1.5m/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.