How to use the Water Tank Calculator
- 1 Choose rectangular or round.
- 2 Enter the length or diameter and width.
- 3 Enter the water depth.
- 4 Optionally enter the number of people.
Worked example
A 6 × 5 ft rectangular tank with water 5 ft deep. It holds 150 cft, about 934 imperial gallons or 4,248 litres. A family of six using 120 litres each a day would have about 5.9 days of water.
Features
Gallons and litres
Imperial gallons, as used in Pakistan, and litres.
Any shape
Rectangular or round tanks.
Days of water
Based on 120 litres per person a day.
When to use it
Overhead tanks
Check the size of a roof tank.
Underground tanks
Plan a new underground tank.
Water tankers
Know how many tankers fill your tank.
Building a house
Size tanks for your family.
Frequently asked questions
How many gallons are in a cubic foot?
About 6.23 imperial gallons or 28.3 litres.
What size tank does a family need?
A family of six using 120 litres each needs about 720 litres a day, so a 500 to 1,000 gallon tank gives a few days' storage.
How big is a water tanker?
Common tankers carry 1,000, 2,000 or 3,000 gallons.
Should I measure full height?
Use the water depth, not the full tank height, since tanks are rarely filled to the top.
How often should tanks be cleaned?
At least twice a year to keep water safe.
Is a plastic tank's capacity printed?
Yes. Plastic tanks are sold by capacity in gallons or litres.
What size overhead tank is common?
Many houses use 500 to 1,000 gallon overhead tanks, filled from an underground tank.
How do I measure a round tank?
Measure the inside diameter and water depth in feet.
Do UK and US gallons differ?
Yes. An imperial gallon is 4.546 litres and a US gallon is 3.785 litres.
How often should I check for leaks?
Check tanks and pipes regularly, as leaks waste water and damage walls.
How do I size an underground tank?
Plan for two to three days of use. A family using 700 litres a day would need about 1,500 to 2,000 litres, around 350 to 450 gallons.
What material is best for tanks?
Plastic tanks are light and easy to install; concrete tanks are common for underground storage. Both need clean covers.
How long does it take to fill a tank?
It depends on the water supply pressure and motor size; a small motor may fill 1,000 gallons in an hour or two.
Can I calculate a tanker's capacity?
Yes. Measure the tank and use the rectangular or round option.
Results are estimates based on the official rates linked above. Confirm important figures with the issuing authority or a qualified adviser before you act on them.
Reviewed by ToolsUnlocked Team · Last updated