Find the right pipe diameter for a given water flow rate, using the standard flow-velocity engineering formula.
Uses the standard flow-continuity formula D = √(4Q ⁄ πV). Rounded up to the nearest standard commercial pipe size — never down, so flow isn't restricted.
This is the exact fluid-mechanics continuity equation relating flow rate (Q), pipe cross-sectional area, and flow velocity (V) — it's how pipe diameters are sized in any plumbing or hydraulic system, not a rule of thumb.
Water moving too fast through a pipe causes noise, water-hammer, and erosion at fittings over time; too slow wastes pipe material and money. 1.5–2.5 m/s is the standard target range for residential water supply pipework — pick 1.5 m/s for pipework near bedrooms where noise matters more.
As a rough reference: a single bathroom group (basin + shower + WC) typically needs 25–35 L/min of simultaneous supply capacity; a kitchen tap needs about 10–15 L/min. For a whole house, add up the groups likely to run at the same time rather than every fixture in the house — not all fixtures run simultaneously.