Interactive Calculator · 2026
Sump Tank Size Calculator
Size the underground sump — the main store that buffers your home against erratic municipal supply. Enter how many people live there, their daily water use and how many days of supply the sump must hold — get the storage capacity in litres and the built volume in m³.
Storage volume (m³) by days of supply held — more days, bigger tank
Your household demand
People the sump must supply through a supply gap.
Litres per capita per day. NBC 2016 uses ~135 LPCD for dwellings with full plumbing; flats with pools or large gardens run higher.
How many days of demand the sump must buffer. 1–2 days suits reliable supply; go higher only where cuts are long and frequent.
Storage volume by days of supply
How the required tank grows with every extra day of resilience you demand.
At 675 L/day of demand, holding 2 days needs about 1.35 m³ of net storage. More days buys resilience against long supply cuts — but a bigger tank costs more, and water that sits too long can go stagnant.
This is the underground store. The overhead tank (OHT) typically holds only a fraction of a day and is refilled from here — size it separately with the overhead tank calculator, then verify both against your actual supply reliability.
How this is calculated
- Daily demand = occupants × LPCD = 5 × 135 = 675 L/day.
- Sump capacity = daily demand × days of storage = 675 × 2 = 1,350 L = 1.35 m³.
- Suggested built volume = capacity + ~12% freeboard = 1.35 × 1.12 = 1.51 m³ — allowing for the air gap, dead storage below the pump inlet and silt.
Indicative sizing for concept planning. LPCD and days of storage are typical starting figures, not binding minimums — tune them to your supply pattern and confirm with a qualified consultant and NBC 2016 Part 9 before procurement.
Frequently asked questions
- How does the sump tank size calculator work?
- It first finds your daily demand by multiplying the number of occupants by the water use per person (LPCD). It then multiplies that daily demand by the number of days of storage you want the sump to buffer, giving net capacity in litres and cubic metres. It also suggests a built volume about 12 percent larger to allow for freeboard, the air gap and dead storage below the pump inlet.
- What LPCD and days of storage should I enter?
- For a home with full internal plumbing, NBC 2016 uses roughly 135 litres per person per day, so 135 LPCD is a sensible default; homes with pools or large gardens run higher. For days of storage, 1 to 2 days suits areas with reliable municipal supply, while 3 or more days makes sense only where cuts are long and frequent. More days means a bigger, costlier tank and water that can sit longer.
- How accurate is the sump size and should the overhead tank be included?
- The result is indicative for concept planning, not a binding minimum. This tool sizes only the underground sump; the overhead tank usually holds a fraction of a day and is refilled from the sump, so size it separately. Tune LPCD and days of storage to your actual supply pattern and confirm the final design with a qualified plumbing consultant and NBC 2016 Part 9 before procurement.
Related Guides — Deep-dive reading
Underground Water Sump Tanks in India: Sizing, Waterproofing and Safe Placement
The below-ground reservoir that catches municipal and borewell water at ground level before a pump lifts it to your overhead tank — how it fits the supply chain, why waterproofing is make-or-break, how big to build it, where to keep it away from the sewer, and how to keep the pump from running dry.
PlumbingWater Storage Tanks Guide for India: Sump, Overhead, Sizing, Materials & Fittings
The master overview of how an Indian home stores water — why storage exists at all, the sump to pump to overhead-tank to gravity chain, how much to hold, underground versus overhead placement, plastic versus RCC versus steel, food-grade and hygiene, the inlet-outlet-overflow-vent-washout fittings, and cleaning at a glance.
PlumbingComplete Guide to Residential Plumbing in India: Supply, Drainage, Pumps & Storage
The homeowner-and-architect deep dive into a house's plumbing — how water enters, how cold and hot water reach every tap, how waste and rain leave, and how pumps and tanks tie it all together, sized in real Indian numbers.
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