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Water Tank Size Calculator

Size your overhead tank from household demand — NBC norms, not guesswork.

Water● Free Formula shown Rates dated
Quick Answer

Indian codes (NBC 2016 / IS 1172) size domestic water demand at 135 litres per person per day for homes with full flushing plumbing. A family of four therefore uses ~540 L/day, so a 750 L overhead tank covers one day comfortably; households on irregular or borewell supply should store 2–3 days, pointing to 1,500–2,000 L. Enter your household below to get the litres and the standard tank size to buy.

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Runs entirely in your browser — nothing you enter is uploaded.

The Formula

Tank size = people × litres per person per day × days of storage, rounded up to a standard tank size

The 135 L/person/day figure is the code norm, chosen visibly as an input rather than hidden in the maths — pick 90 L for minimal-plumbing homes or 180 L for high-use households and the whole working updates.

Assumptions & Wastage

  • Demand norms from NBC 2016 / IS 1172: 135 lpcd for residences with full flushing systems; the code's own breakdown is drinking 5 + cooking 5 + bathing 55 + clothes washing 20 + utensils 10 + house cleaning 10 + flushing 30
  • The result is domestic storage only — garden, car washing, construction curing and firefighting storage are extra
  • Suggested sizes follow the standard rotomoulded tank ladder: 500, 750, 1000, 1500, 2000, 3000, 5000 L and up
  • Where a sump + overhead tank combination is used, the total across both should meet the storage figure; the overhead tank alone can then be smaller

Worked Examples

Family of 4, municipal supply, 1 day of storage

  1. Daily demand: 4 people × 135 L/person/day = 540 L/day
  2. Storage: 540 L/day × 1 day = 540 L
  3. Next standard tank size: 750 L

Load this example in the calculator

Family of 6 on borewell, 2 days of storage

  1. Daily demand: 6 people × 135 L/person/day = 810 L/day
  2. Storage: 810 L/day × 2 days = 1,620 L
  3. Next standard tank size: 2,000 L

Load this example in the calculator

Rates & Model Data Used

This calculator uses no market rates — it is pure arithmetic on the inputs you enter, with every constant published in the Assumptions section above.

How to Use This Calculator

  1. Count everyone. Include live-in help and long-stay guests — the norm is per person, and undercounting is the usual reason tanks run dry.
  2. Pick the usage norm. 135 L is the code standard for homes with full flushing plumbing. Choose 90 L for minimal plumbing, 180 L if your household demonstrably runs high.
  3. Decide the storage days. Reliable daily supply needs 1 day. Alternate-day municipal supply, summer cuts or borewell dependence justify 2–3 days.
  4. Buy the suggested size. Tanks come in standard sizes, so the calculator rounds up for you. Slightly over is fine; grossly over means stagnant water and a heavier roof load.

Frequently Asked Questions

What tank size does a family of 4 need?
About 540 L/day at the NBC 2016 norm of 135 litres per person per day — so a 750 L overhead tank for daily municipal supply, or 1,000–1,500 L where supply is irregular. With an underground sump doing primary storage, a 500–750 L overhead tank plus a 1,000 L+ sump is the common split.
Why 135 litres per person per day?
It is the NBC 2016 / IS 1172 planning norm for residences with full flushing systems, built up as: bathing 55 L, clothes washing 20 L, flushing 30 L, utensils 10 L, house cleaning 10 L, cooking 5 L and drinking 5 L. Homes without full flushing plumbing are normed lower, at 70–100 lpcd.
Should I use an overhead tank, an underground sump, or both?
Both, in most Indian cities: the sump collects whenever supply arrives (municipal timing is rarely convenient) and holds 1–2 days of demand; a pump lifts to a smaller overhead tank — typically half a day to a day — which gravity-feeds the house. Single overhead tanks suit places with reliable pressure and daily supply.
How big is a 1,000 litre tank physically?
1,000 L is exactly 1 m³. A typical rotomoulded 1,000 L tank is roughly 1.1 m in diameter and 1.1–1.2 m tall, and weighs about 1,000 kg when full — which is why tank platforms on roofs need to sit over beams or walls, not mid-slab. Always check the slab or frame can take the full weight.
Does the calculation cover gardening, car washing or construction?
No — the code norm is domestic use only. A small garden or regular car washing typically adds 30–50 L per day; pick the 180 L option or add a dedicated allowance rather than letting outdoor use eat the household's buffer.
Is a bigger tank always better?
No. Water stored beyond about 3 days can stagnate and lose residual chlorine, oversized rooftop tanks impose serious structural loads, and dead storage is money spent to make water quality worse. Size to genuine need plus a sensible buffer — the days-of-storage input is the honest lever.
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Sources & Limitations

What this calculator does not model

  • Sizes domestic storage only — firefighting storage, rainwater harvesting and irrigation are separate calculations
  • Does not size the pump, pipes or float valves; it sizes the tank
  • Apartment buildings follow their own municipal and NBC provisions — this is for individual homes
  • Structural adequacy of the tank platform must be checked by an engineer for anything above ~1,000 L on a roof