Estimate the recommended pipe size for a plumbing or water supply line based on flow rate, target velocity, pipe length, pressure drop, fixture demand, and safety factor. Use this pipe size calculator for water lines, fixture branches, irrigation piping, pumps, and general plumbing planning.
Flow rate and velocity:
The calculator converts the flow rate to cubic feet per second, divides it by target velocity to find pipe area, then converts that area into an estimated inside diameter.
Fixture demand:
The calculator multiplies fixture count by flow per fixture and simultaneous use percentage, then applies a safety factor.
Pressure drop:
The calculator estimates a pipe size using a Hazen-Williams style relationship between flow, pipe length, pipe material, and allowed pressure drop.
A pipe size calculator helps estimate whether a plumbing line is large enough to carry the needed water flow without excessive velocity or pressure loss.
It can help compare flow rate, pipe diameter, water velocity, pressure loss, fixture demand, safety factor, and common nominal pipe sizes.
Your result shows an estimated inside pipe diameter, a suggested nominal pipe size, adjusted flow rate, target velocity, estimated pressure loss, and fixture demand. These are planning estimates only. Final pipe sizing should account for plumbing code, fittings, valves, elevation, water pressure, pipe material, pipe condition, and the full system layout.
Estimate the needed flow rate, choose a target water velocity, calculate the required pipe area, then convert that area into an inside diameter.
A larger pipe can reduce friction loss and velocity, which may allow more usable flow if pressure and supply capacity are available.
A pipe that is too small can increase velocity, pressure loss, noise, and poor fixture performance.
No. This calculator gives a planning estimate. Final pipe sizing should follow local plumbing code and account for the complete system.