Water Pipes Sewage Gravity Channels Water Network & Connection Pipe slopes Pipe loads Well buoyancy DHW cylinder sizing

Register to start using the calculator!

One account unlocks every calculator on the site — try it free for 5 days, no card required.

Building usage type:

Sanitary Fixtures

Washbasin

Bidet

Shower without plug

Shower with plug

Urinal with tank

Urinal with flush valve

Wall-hung urinal

Bathtub

Kitchen sink

Dishwasher

Washing machine up to 5kg

Washing machine up to 12kg

WC with 6.0l tank

WC with 7.5l tank

WC with 9.0l tank

Floor drain DN50

Floor drain DN70

Floor drain DN100

New — from the makers of KalkulatorPro

Designing a sewer network? Build the longitudinal profile and a CAD-ready DXF.

Paste your coordinates — Altivo computes slopes and elevations, and the DXF export drops straight into AutoCAD. No install, no dongle, in the browser.

Try Altivo for free

Sanitary sewage calculator — design flow rate per PN-EN 12056-2

Professional calculator for determining wastewater flow rates in internal sanitary drainage systems. Calculations are performed for System I according to PN-EN 12056-2 'Gravity drainage systems inside buildings'. Based on the building usage type (coefficient K) and a list of sanitary fixtures, the calculator determines the sum of unit discharges ΣDU and the design flow rate Qww. A tool for plumbing designers, installers and building engineers.

How to use the calculator in 3 steps

Select the type of drainage system usage — this determines the frequency coefficient K: intermittent use K = 0.5 (apartments, offices), periodic K = 0.7 (hospitals, schools, hotels), collective K = 1.0 (public toilets and showers), special K = 1.2 (laboratories).

Add sanitary fixtures connected to the pipe section. For each fixture, specify its type and quantity. The calculator automatically reads unit discharges DU from PN-EN 12056-2 and calculates the sum ΣDU.

Read the design flow rate Qww [l/s], calculated using the formula Qww = K × √ΣDU. Use this value to size the discharge pipe — the gravity sewer calculator will help with diameter selection.

Calculation formula and PN-EN 12056-2 standard

The design wastewater flow Qww is determined by the formula: Qww = K × √ΣDU [l/s], where K is the frequency coefficient depending on the usage type, and ΣDU is the sum of unit discharges of all sanitary fixtures connected to the pipe section.

System I (partially filled branch connections) — the most common system used in Poland. Sanitary fixtures are connected to partially filled branches (fill ratio 0.5), which lead to a single drainage stack. The system provides ventilation through a vent stack above the roof.

Unit discharges DU [l/s] per fixture according to PN-EN 12056-2: wash basin — 0.5, kitchen sink — 0.8, bathtub — 0.8, shower (with tray) — 0.6, WC with 6 l cistern — 2.0, WC with 9 l cistern — 2.5, washing machine (up to 6 kg) — 0.8, dishwasher — 0.8, bidet — 0.5, urinal with cistern — 0.5.

Note: Unit discharges DU per PN-EN 12056-2 differ from normative outflows qn per PN-92/B-01706 used for water supply pipe sizing. Do not confuse them.

Frequency coefficient K — types of installation usage

The K coefficient reflects the probability of simultaneous use of sanitary fixtures and has a crucial impact on the calculated flow:

K = 0.5 — intermittent use: apartments, guest houses, offices. Fixtures used sporadically, low simultaneity.
K = 0.7 — periodic use: hospitals, schools, restaurants, hotels. Fixtures used more frequently, at specific times of day.
K = 1.0 — collective use: public toilets and showers. Many fixtures operating simultaneously.
K = 1.2 — special use: laboratories. Highest simultaneity coefficient.