Water Tank Capacity Calculator
Determine total water volume, storage capacity in Litres & Gallons, and days of water supply for your family or building.
Tank Geometry
Family & Usage Needs
13,592 Litres
Complete Guide to Water Tank Size & Capacity Sizing
Designing an underground water sump (UGT) or selecting an overhead PVC water tank (OHT) requires accurate volumetric calculations. Sizing a water tank properly ensures your household or residential apartment never runs dry even during extended municipal water cutoffs.
Water Tank Formulas
- Rectangular Volume = Length × Width × Depth
- Cylindrical Volume = π × (Diameter ÷ 2)² × Height
- 1 Cubic Foot (CFT) = 28.317 Litres (7.48 US Gallons)
- 1 Cubic Meter (m³) = 1,000 Litres (264.17 US Gallons)
- Effective Capacity = Total Litres × (1 - Air Margin %)
- Days of Backup = Effective Litres ÷ (People × Daily Need)
Daily Water Demand Standards (IS 1172)
- Drinking & Cooking: 10 Litres / person / day
- Bathing & Sanitation: 55 Litres / person / day
- Flushing: 30 Litres / person / day
- Washing Utensils & Clothes: 40 Litres / person / day
- Total Standard Indian Household: 135 Litres / head / day (LPCD)
Frequently Asked Questions (FAQs)
What size overhead tank is best for a family of 4?
For a family of 4 consuming 135 Litres per person per day (total 540 Litres daily), a standard 1,000 Litre or 1,500 Litre overhead cylindrical tank provides 2 to 3 full days of emergency water reserve.
What is the ideal ratio between Underground Sump and Overhead Tank?
Civil engineering best practice recommends sizing the underground sump to hold 1.5x to 2x the capacity of the overhead tank. For instance, if your rooftop tank is 1,000 Litres, construct an underground sump of 2,000 to 3,000 Litres to buffer municipal supply fluctuations.
Why must we leave 10% to 15% freeboard margin in water tanks?
Freeboard is the empty air space between the top edge of the tank and the maximum water level set by the float ball valve. It prevents overflow splashing, accommodates structural breathing, and leaves space for inlet pipe fittings.