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Water pipe diameter selection

Building type

Pipe type

Max speed [m/s]

Sanitary fixtures

Basin

Sink

Rinser

Bathtub

Shower

Washing machine

Dishwasher

Urinal

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Water pipe sizing calculator — calculations according to PN-92/B-01706

Professional calculator for sizing water supply pipes in internal plumbing installations. Calculations are performed according to the Polish standard PN-92/B-01706 — from listing normative outflows of sanitary fixtures, through determining the design flow rate with simultaneity factors, to selecting a commercial pipe diameter meeting velocity criteria. The calculator supports residential and public buildings, taking into account different building types and their corresponding calculation formulas. A tool for plumbing designers, installers and building engineers.

How to use the calculator in 3 steps

Select the building type (residential, office, hotel, hospital, etc.) — this determines the calculation formula and the simultaneity factor for sanitary fixtures.

Enter the number and type of sanitary fixtures supplied by the pipe section. The calculator will automatically read normative outflows qn from the PN-92/B-01706 standard and calculate the total outflows Σqn and design flow rate qobl.

Read the results: the calculator will suggest a pipe diameter meeting the flow velocity criterion. For each diameter you will see the actual water velocity [m/s] and pressure drop [kPa]. Check whether the available pressure at the service connection is sufficient.

Building types and calculation formulas

Residential buildings — the PN-92/B-01706 standard provides three formula ranges depending on the total normative outflows Σqn. For a typical single-family house with two bathrooms, Σqn is approximately 1.0–1.5 dm³/s, and the design flow after applying the simultaneity factor is only 0.5–0.7 dm³/s.

Public buildings (offices, hotels, hospitals, schools) — use different formula sets with higher simultaneity factors, as more fixtures operate simultaneously in these buildings. The calculator automatically selects the appropriate formula after choosing the building type.

The building type selection significantly affects results — the same set of fixtures produces different design flows for residential and hotel buildings.

Recommended design values for water supply systems

The following values are based on the PN-92/B-01706 and DIN 1988 standards and form the basis for proper pipe sizing:

Velocity in fixture connections: up to 1.5 m/s (PN-92) / up to 2.0 m/s (DIN 1988) — limiting hydraulic noise in occupied rooms.
Velocity in risers: up to 1.5 m/s (PN-92) / up to 2.0 m/s (DIN 1988) — in practice, design with 0.8–1.2 m/s for acoustic comfort.
Velocity in distribution pipes: up to 1.0 m/s (PN-92) / up to 1.5 m/s (DIN 1988) — lower velocities for longer sections.
Velocity in service connections: up to 1.0 m/s (PN-92) / up to 1.5 m/s (DIN 1988).
Minimum pressure at fixture outlet: 0.05 MPa (0.5 bar) for most fixtures. When sizing pipes, verify that the available pressure at the service connection covers linear, local and hydrostatic pressure losses.
Pay attention to pipe material — at the same outer diameter, different materials have different wall thicknesses: PP 25 mm pipe (ID = 16.6 mm) will carry significantly less water than PEX 25 mm (ID = 20.0 mm). The calculator accounts for actual internal diameters.