Interactive Calculator · 2026
STP Capacity Calculator
Size a sewage treatment plant for any building. Pick a building type, enter the occupancy, and get the required STP capacity in KLD (kilolitres per day) — the number every STP design starts from.
Water demand → sewage generated → installed STP capacity
Your building
NBC 135 LPCD, full plumbing
Share of water supplied that becomes sewage — CPCB/NBC take ≈80%.
Safety headroom over average daily flow before rounding to a standard plant size.
Treated water you can reuse
A well-run STP recovers ≈43.2 KLD of reusable water — a typical allocation:
Reusing this water for flushing, landscape and cooling can cut a building's freshwater purchase by roughly a third — often the fastest-paying part of the whole system.
Only the surplus that cannot be reused is discharged, and by law it must meet the treated-water standards first.
How this is calculated
- Water demand = occupancy × LPCD = 400 × 135 = 54 KLD.
- Sewage generated = water demand × 80% return = 43.2 KLD.
- STP capacity = sewage × (1 + 15% margin), rounded up to a standard plant size = 50 KLD.
Indicative sizing for concept planning per NBC/CPCB norms. A detailed design must also fix peak factor, tank volumes and equipment — confirm with a qualified consultant before procurement.
Related Guides — Deep-dive reading
STP for Shopping Malls: Mixed Loads, Big Reuse
Why a mall's wastewater is unlike any other building's — a punishing mix of food-court grease, washroom peaks and huge cooling-tower thirst — and how to size, site and choose an STP that turns all of it back into usable water in the basement.
Sewage Treatment PlantsApartment STP Planning Guide: Sizing, Space & Compliance
How to plan a sewage treatment plant for an apartment complex — sizing it from occupancy, choosing the right technology, finding space for it, plumbing it for reuse, and keeping it compliant and running for years.
Sewage Treatment PlantsSTP for Hotels: High Per-Guest Loads, FOG & Water Reuse Explained
Why hotel wastewater is heavier and swingier than an apartment's, which STP technology (MBBR vs MBR) actually fits, how to size for peak occupancy, and where the treated water pays for itself — in laundry, cooling and landscape.
Sewage Treatment PlantsRelated Tools — You may also find these useful
BOD Load Calculator
Calculate the organic (BOD) load on an STP in kg/day and the removal efficiency required to meet discharge norms from flow and inlet/outlet BOD.
STP CalculatorCommercial STP Planner
Plan a commercial building's sewage treatment plant from occupancy — get water demand, sewage generated, recommended STP capacity in KLD, the best-fit technology and reusable treated water.
PlannerHydraulic Retention Time (HRT) Calculator
Compute a reactor or tank's hydraulic retention time from its volume and daily flow, and benchmark it against recommended ASP, MBBR and SBR ranges.
STP Calculator