Interactive Calculator · 2026
Drainage Fixture Unit Calculator
Total the drainage fixture units (DFU) of a home's sanitary fixtures and get an indicative drain and soil stack size. Enter how many WCs, basins, sinks, showers, floor drains and washing machines you have — see the total DFU load and recommended pipe sizes.
DFU contribution by fixture type
Count your fixtures
Highest DFU load per fixture.
Lavatory / hand basins.
Kitchen and utility sinks.
Shower stalls and bath tubs.
Bathroom / balcony floor traps.
Automatic clothes washers.
Per-fixture DFU values are typical figures and vary by code — NBC 2016 Part 9 and the IPC assign slightly different loads. Treat these as indicative for concept planning.
DFU contribution by fixture
WCs dominate the load — a single WC carries as much DFU as several basins.
Your fixtures total 29 DFU. On the indicative thresholds below that points to a 100 mm horizontal drain and a 100 mm stack soil stack.
The stack and horizontal drain can differ because they carry the load at different angles — always confirm both against the drainage table for your code.
How this is calculated
- Total DFU = Σ (count × DFU per fixture) = 2×6 + 2×1 + 1×2 + 2×2 + 3×2 + 1×3 = 29 DFU.
- Recommended sizes from an indicative lookup on total DFU: ≤8 → 75 mm branch, ≤24 → 100 mm, ≤42 → 100 mm stack, ≤60 → 125 mm, else 150 mm. Your 29 DFU → horizontal drain 100 mm, soil stack 100 mm stack.
DFU values and sizing thresholds are indicative and vary by code. This is a concept-planning estimate — verify every pipe size against NBC 2016 Part 9 / IPC drainage tables and a qualified consultant before procurement.
Frequently asked questions
- What is a drainage fixture unit (DFU) and how does this calculator work?
- A drainage fixture unit is a standard number that represents the discharge load a plumbing fixture puts on a drain. This tool multiplies how many of each fixture you enter by a typical DFU value per fixture, then adds them up. A WC counts most, while basins count least. The total DFU is then matched to an indicative drain and soil stack size.
- What inputs do I need to use it?
- Just enter counts of the sanitary fixtures in your home: WCs, wash basins, kitchen sinks, showers or bathtubs, floor drains and washing machines. Sensible defaults are already filled in for a typical two-toilet home, so you can start from those and adjust. The total DFU and recommended horizontal drain and stack sizes update instantly as you change any count.
- How accurate are the recommended pipe sizes?
- Treat them as indicative for concept planning only. Both the per-fixture DFU values and the size thresholds vary by code, and NBC 2016 Part 9 and the IPC assign slightly different loads. Actual sizing also depends on pipe slope, venting and simultaneous use. Always confirm every drain and stack diameter against the drainage tables in NBC 2016 Part 9 and a qualified plumbing consultant before you procure or build.
Related Guides — Deep-dive reading
Plumbing-Efficient Bathroom Layout India: Single Wet Wall, Back-to-Back & Stacked Bathrooms
How to arrange bathroom fixtures to minimise pipe runs — the single wet wall, back-to-back and stacked bathrooms, shared shafts — with sizes in mm, rupee savings, and the drainage-slope rules that cut cost and leak risk in an Indian home.
BathroomsDomestic Water Distribution in India: Piping Cold Water to Every Fixture
How water travels from the overhead tank or pump to every tap, shower and cistern in an Indian home — trunk-and-branch versus manifold layouts, pipe sizing by simultaneous demand, pressure balancing across floors, isolation valves per wet area, and how to kill water hammer.
PlumbingDrainage 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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