How tank capacity is calculated
For a rectangular tank the volume is simply length × width × height. For a cylindrical tank it is π × radius² × height, where the radius is half the diameter. All measurements are converted to metres first, so the volume comes out in cubic metres; multiplying by 1,000 gives litres, the unit most people use for water storage.
Litres, cubic metres and gallons
One cubic metre holds exactly 1,000 litres. A litre is about 0.264 US gallons or 0.220 imperial gallons, so the same tank reads differently depending on which gallon you mean. This tool shows all of them so a 1,000-litre tank is instantly readable as 1 m³, roughly 264 US gallons or 220 imperial gallons.
Sizing a domestic water tank
A common rule of thumb for household storage is around 100–150 litres per person per day for all uses. A family of four planning one day of reserve therefore needs roughly a 500–600 litre tank, while overhead tanks on Indian rooftops are frequently 500, 1,000 or 2,000 litres. Measuring your existing tank and comparing it against daily demand tells you how long your reserve will actually last.
Frequently asked questions
How do I find the capacity of a round tank in litres?
Measure the inside diameter and height, switch to the Cylindrical tab and enter both. The tool computes π × radius² × height and converts the result to litres automatically.
Does this give the exact fill capacity?
It gives the full geometric volume from the internal dimensions. Real usable capacity is slightly less because tanks are rarely filled to the very brim and wall thickness reduces the interior slightly.