Whether you have your own water tank or a tank for your business, it’s helpful for you to know how much water it can hold.
A continuous supply of water is essential to keep a building running smoothly, so knowing the capacity of your water tank is essential to keep up with the demand.

There are two different ways of calculating your water tank capacity in liters, depending on the shape of your tank – the calculations differ for rectangular tanks compared to cylindrical tanks.
This article will teach you how to do these calculations, as well as calculate water demand, so you can be sure that your tank can hold the appropriate amount of water.
How to Calculate Water Demand in Liters
As a standard, around 135 liters of water is necessary for each person, each day. On average, we use 5 liters of water for drinking, 5 liters for cooking, 85 liters for bathing and using the toilet, 30 liters for doing laundry, and 10 liters for cleaning.
With this information in mind, we can easily calculate your daily water demand.
The equation is simple – just multiply the amount of people that use your property by 135 to find out how many liters of water you need daily. For example, for a family of four, you will need 540 liters of water a day for your household.
If you have a water tank for a business, remove the redundant activities from the equation. For example, if your building doesn’t use washing machines, you can subtract 30 from the 135 liters of water you need daily.
So, if you own an office building that has 100 employees and has no need for washing machines, multiply 105 by 100, and you‘ll find that you need 10,500 liters of water per day.
So, to recap:
- You need 135 liters of water per day per person.
- You need 5 liters of drinking water.
- You need 5 liters for cooking.
- You need 85 liters for bathing and toilet use.
- You need 30 liters for laundry.
- You need 10 liters for cleaning.
- 135 x people per day = the amount of liters of water needed per day.
- Subtract liters that aren’t needed in your building from 135 if necessary.
How to Calculate Capacity of a Rectangular Water Tank
Calculating the capacity of a rectangular water tank is much easier than calculating the capacity of a cylindrical one. It involves finding the volume of the tank with an easy equation.
Knowing the volume will allow you to convert this measurement into liters.
First, you need to measure the length, width and height of your water tank in meters.
Measure the longest side horizontally for the length, the shortest shortest side horizontally for the width, and the vertical distance between the top and bottom of the tank for the height.

Now to calculate the volume of your water tank. You need to take the measurements for the length, width and height of your water tank and multiply these values together. This will give you the volume of your water tank in cubic meters.
So, for example, if the length of your tank is 2 meters, the width is 1 meters, and the height is 0.5 meters, the volume of your tank would be 1 cubic meter.
Next, you need to convert the volume of your tank from cubic meters to liters. Simply multiply the volume of your water tank by 1000 and you will be left with the correct conversion. In this case, your tank’s volume in liters would be 1000.
So, to summarize this:
- Measure the length, width and height of your tank in meters.
- Length x width x height = volume in cubic meters.
- Volume in cubic meters x 1000 = volume in liters.
How to Calculate Capacity of a Cylindrical Water Tank
Finding out the capacity of a cylindrical water tank is more complex than finding that of a rectangular tank. You should use a scientific calculator for this equation to find the volume of your tank before converting it into liters.
First, you need to find the height of your water tank and the area of your tank’s base in meters. To find the height, simply measure your tank vertically from top to bottom. Calculating the area of the base is more complicated.
The formula for the area of a circle is pi multiplied by the radius squared. So, first measure the radius of the base of your tank. This is the horizontal length in meters between the middle of the base and the edge of the base.
Once you’ve done this, square that number and you’ll be left with the diameter. Finally, multiply this number by pi and you’ll have calculated the area of your tank’s base in square meters.
So, as an example, if the radius of your tank is 2 meters and you square it, the diameter will be 4 meters. Multiply this figure by pi and you’ll get 12.56 square meters.
Now that you have the height of your tank and the area of the circular base of your tank, you need to multiply these figures together and round your answer to a whole number with no decimal places.
After you’ve done this, you will have the volume of your water tank in cubic meters and.
So, if the area of the base is 12.56 square meters and the height of your tank is 10 meters, the volume of your tank will be 125 cubic meters after rounding to the nearest whole number.
Finally, multiply the volume of your tank in cubic meters by 1000, and you will get the volume of your tank in liters. For the example used, you’re tank’s volume would be 125,000 liters
So, in summary:
- Measure the height of your tank in meters.
- Calculate the area of the base of your tank with x radius2.
- Area x height = volume in cubic meters.
- Volume in cubic meters x 1000 = volume in liters.
Conclusion
With these formulas, a calculator, and a tape measure, you can calculate the capacity of your water tank in liters yourself easily. Use this guide to correctly measure the volume of your tank and the water demand for your property.
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