Interactive Calculator · 2026
Overhead Water Tank Size Calculator
Size the overhead (roof) water tank for a home. Enter the number of occupants, the water use per person and how much of the day's water you want held overhead — get the daily demand, the required OHT capacity and the nearest standard poly-tank size to buy.
Required capacity → nearest standard poly-tank size
Your household
People the tank must supply.
Litres per capita per day. NBC / CPHEEO takes ~135 LPCD as a typical domestic figure for homes with full plumbing.
Fraction of the day's water kept in the roof tank — the rest is stored in the underground sump and pumped up as needed. Half a day (0.5) is a common split.
Required capacity vs standard tank size
Poly tanks come in fixed sizes, so we round the requirement up to the nearest one you can actually buy.
The overhead tank is normally only part of a day's storage — here it holds 338 L, rounded up to a 500 L standard tank. The remaining daily water sits in the underground sump and is pumped up on demand.
A full roof tank is a heavy point load — keep the structural load in mind and verify the slab with a structural engineer for large tanks. This is different from sizing a whole-storage sump that holds the full day (or more) at ground level.
How this is calculated
- Daily demand = occupants × LPCD = 5 × 135 = 675 L per day.
- Required OHT capacity = daily demand × share held overhead = 675 × 0.50 = 338 L.
- Recommended tank = smallest standard poly-tank ≥ required capacity = 500 L (from 500 / 750 / 1000 / 1500 / 2000 / 3000 / 5000 L).
Indicative sizing for concept planning. Peak-demand patterns, pump top-up frequency and supply reliability all shift the split between overhead tank and sump — confirm against NBC 2016 Part 9 and a qualified consultant before procurement.
Frequently asked questions
- How does this overhead tank size calculator work?
- It first finds your daily water demand by multiplying the number of occupants by the water use per person (LPCD). It then multiplies that daily demand by the share of the day you want held on the roof to get the required overhead capacity, and rounds up to the nearest standard poly-tank size actually sold in India, from 500 up to 5000 litres.
- What values should I enter for occupants, LPCD and day share?
- Enter the real number of people the tank serves. For water use per person, NBC and CPHEEO take roughly 135 LPCD as a typical domestic figure for homes with full plumbing, so start near there. For share of the day held overhead, half the day (0.5) is a common split, with the rest kept in the underground sump and pumped up as needed.
- How accurate is the recommended tank size?
- Treat it as indicative sizing for concept planning, not a final specification. Peak-demand patterns, pump top-up frequency and supply reliability all shift the split between overhead tank and sump. A full roof tank is a heavy point load, so confirm the slab and overall design against NBC 2016 Part 9 and a qualified structural or plumbing consultant before you buy.
Related Guides — Deep-dive reading
Overhead vs Underground Water Tank: Which Do You Need in India?
A fair, India-first head-to-head: an overhead tank gravity-feeds your taps but holds little; an underground sump stores huge volumes from erratic supply but needs a pump. Capacity, pressure, cost, cleaning, contamination — and why most Indian homes quietly run both.
PlumbingUnderground 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.
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