Pipe Size Calculator
Find the right water pipe diameter (nominal bore) for a given flow and design velocity — the everyday check for plumbing risers and mains. Adjust the inputs, then get an engineered plumbing design.
Your flow
Sizes the pipe on the velocity method (area = flow ÷ velocity). Typical water velocity is 1.0–2.5 m/s; a full design also checks friction loss, water hammer and noise.
Get an engineered plumbing design — free
Our public-health engineers will size the full pipe network, pumps and pressure zones for your building. We'll attach the estimate above automatically.
Your request is in
Thanks! Our plumbing team will send your tailored pipe & pump design within one business day.
Indicative estimates only — not a binding design. Actual pipe sizing depends on simultaneous demand, friction loss, material, pressure and water-hammer limits.