Water Tank Capacity Calculator (Litres and Days)
Multiplies tank length, width and height to give the capacity in litres and estimates how many days that water lasts.
Recent
Formula
How the calculation works
The tool multiplies the tank length, width and height in metres to get the volume in cubic metres.
It then multiplies that volume by one thousand, because one cubic metre holds one thousand litres of water.
Finally it divides the total litres by the daily household usage to return the number of days the tank lasts.
Common mistakes
- Entering dimensions in feet while the formula expects metres, which inflates the litres by roughly thirty-five times.
- Filling the tank to the very top in calculations, when the usable water level usually stays below the overflow pipe.
When to use it
- Size a rooftop tank so it lasts through a full week of household demand.
- Check how many days your current tank covers during a water supply cut.
Worked example
A tank 2 metres long, 1.5 metres wide and 1 metre high holds 3000 litres, and a household using 200 litres a day would get 15 days from it.
Common questions
Why is the tank height so important in this capacity?
The tank capacity is a volume, so height matters as much as length and width; doubling the height doubles the litres it can hold.
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