How does the bathroom drainage pipe calculator size my pipes?

You tick the fixtures your bathroom drains — WC, wash basin, shower or floor trap, bathtub, washing machine — and give the main run length to the stack or chamber. It maps each fixture to a typical waste or soil size, sizes the main stack at 110 mm wherever a WC connects (otherwise a 75 mm waste stack), adds up an indicative fixture-unit load, and works the fall over your run.

What pipe sizes and slopes does it assume for common fixtures?

As indicative rules of thumb it puts a WC on a 110 mm soil line, a wash basin on 32 to 40 mm, a shower or floor trap on 50 to 75 mm, and a bathtub or washing machine on 40 to 50 mm waste. Recommended falls run roughly 1:40 to 1:60, steeper for small waste pipes. Too flat leaves water sitting, too steep can leave solids behind.

How accurate is it and what should I verify?

Treat the results as indicative planning figures that follow general Indian practice, broadly aligned with IS 1172 and NBC 2016 Part 9 rather than exact clauses. Real sizing depends on your full layout, venting, number of floors, discharge and local bye-laws. Confirm every pipe size, trap and gradient against the applicable code and have a licensed plumber review the design before you build.

Drainage Calculator

Bathroom Drainage Pipe Calculator

Pick the fixtures your bathroom drains and the run length to the stack. Get the recommended pipe size and fall/gradient for each, the main stack size and pipe lengths per size. Indicative India 2026 (general IS 1172 / NBC Part 9 practice) — always verify against code and a licensed plumber.

Your fixtures & run

Which fixtures connect?

Main run to stack / chamber (m)

Sizes and slopes are indicative rules of thumb: WC discharges to a 110 mm soil line, basins/showers/baths run on 32–75 mm waste lines, and the main stack is 110 mm wherever a WC connects. Steeper falls suit small waste pipes; too steep can leave solids behind. Confirm every size, trap and vent against local code.

Main soil stack size

0 mm

serving 0 fixtures · recommended fall 1:40 – 1:60 on the main run

Main stack

110 mm

WC connected → soil

Fixture-unit load

indicative discharge units

Main run fall

63 mm

over 3 m @ 1:48

Total pipe

6.9 m

across 3 sizes

Fixture	Pipe size	Type	Min slope
WC / water closet	110 mm	Soil	1:40 – 1:60
Wash basin	32–40 mm	Waste	1:40 (min)
Shower / floor trap	50–75 mm	Waste	1:40 – 1:50
Bathtub	40–50 mm	Waste	1:40 – 1:48
Washing machine	40–50 mm	Waste	1:40

Pipe running length by nominal size (branches + main run). Indicative — confirm with your plumber.

Plan the drainage layout

Sanity-check pipe sizes, traps and venting for this bathroom with DesignAI.

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These pipe sizes, slopes and fixture-unit loadings are indicative and follow general Indian plumbing practice (broadly aligned with IS 1172 and NBC Part 9) — they are not exact code clauses. Actual sizing depends on your full drainage layout, venting, number of floors, fixture discharge and local bye-laws. Always verify every size and gradient against the applicable code and have the design reviewed by a licensed plumber before you build.

Frequently asked questions

How does the bathroom drainage pipe calculator size my pipes?: You tick the fixtures your bathroom drains — WC, wash basin, shower or floor trap, bathtub, washing machine — and give the main run length to the stack or chamber. It maps each fixture to a typical waste or soil size, sizes the main stack at 110 mm wherever a WC connects (otherwise a 75 mm waste stack), adds up an indicative fixture-unit load, and works the fall over your run.
What pipe sizes and slopes does it assume for common fixtures?: As indicative rules of thumb it puts a WC on a 110 mm soil line, a wash basin on 32 to 40 mm, a shower or floor trap on 50 to 75 mm, and a bathtub or washing machine on 40 to 50 mm waste. Recommended falls run roughly 1:40 to 1:60, steeper for small waste pipes. Too flat leaves water sitting, too steep can leave solids behind.
How accurate is it and what should I verify?: Treat the results as indicative planning figures that follow general Indian practice, broadly aligned with IS 1172 and NBC 2016 Part 9 rather than exact clauses. Real sizing depends on your full layout, venting, number of floors, discharge and local bye-laws. Confirm every pipe size, trap and gradient against the applicable code and have a licensed plumber review the design before you build.

Related Guides — Deep-dive reading

Bathroom Drainage India: Waste vs Soil Pipes, Slope, Sizes, Traps & Venting (2026)

How a bathroom's waste and soil pipes actually work — the difference between waste lines (basin, shower) and the soil line (WC), the fall you need, pipe sizes in mm, floor slope to the floor trap, how it all joins the stack, and how traps and venting stop blockages and smells.

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Bathroom Plumbing India: The Complete Guide to Water Supply, Drainage, Traps & Pipes

The whole plumbing picture for an Indian bathroom in one place — the two systems (cold and hot water supply, and waste/soil drainage with its vented SWV stack), traps and the floor trap, slopes and gradients, concealed vs exposed pipework, pipe materials (CPVC/UPVC/PEX/GI) and the overhead-tank pressure reality — with the coordination that must happen before any civil work starts.

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Drainage Systems Guide for Indian Homes: DWV, Traps, Slopes & Stacks

The section pillar for household drainage — the two waste streams, gravity and gradients, traps and the water seal, the soil stack and branch layout, why venting matters, keeping foul and rain separate, and how it all connects to sewer, septic or an STP at the plot boundary.

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