Work out pipe diameter for flow instantly with clear inputs, formula shown and shareable results.
Pipe diameter follows from continuity: area is flow divided by the velocity limit, and diameter is the diameter of a circle with that area. Velocity limits are set by noise and erosion, typically 1.0-1.5 m/s for a distribution main and up to 2.5 m/s for short branches.
Diameter
A = Q / V; D = sqrt(4A / pi)
Design flow
Q design = peak flow x (1 + growth margin)
A = Q / V; D = sqrt(4A / pi). Pipe diameter follows from continuity: area is flow divided by the velocity limit, and diameter is the diameter of a circle with that area.
Up. Rounding down pushes velocity above the limit, and velocity drives both noise and friction loss, which is squared in the pressure penalty.
This calculator takes 3 inputs: Design flow, Maximum velocity, Flow margin for growth. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.