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Water Tank Calculator
Capacity of rectangular and round water tanks in gallons and litres, and the tank size you need for your family.
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About this calculator
Find the capacity of an underground or overhead water tank from its inside size, or the size of tank you need for the number of people in the house.
How it's calculated
- Volume (cft) = length × width × water depth, or π × d² ÷ 4 × depth
- 1 cft = 6.229 imperial gallons = 28.32 litres
- Storage = people × gallons per day × days
What size tank for a 5 marla house?
For 6 people at 30 gallons a day and 2 days' storage: about 360 gallons — for example 5 × 5 ft with 2½ ft of water.
Results are calculated from the values you enter using standard formulas. Download the PDF to keep a record. For certified testing, design or construction, talk to our engineers.
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