A Tank Volume Calculator will b able to help you determine whether or not the tank you are getting is sufficient for your intended use. It is important to keep in mind that water tanks come in many shapes and sizes, therefore, you need to ensure that you know the volume before purchasing.

Water Shortage and the need for water storage

Water is one of the most important natural resources. Humans need copious amounts of water for every-day living at home, work and in public. Furthermore, major industries use water for cooling, cleaning and so much more. That is why the water shortage in South Africa is a major concern. At a later stage we will review the water shortage problem in-depth in a blog post, but for now, let’s look at the importance of water in South Africa.

We discussed the Importance of water in a previous post: The Importance of Water. In the post, we discussed the amount of water used by a single person in South Africa.

We concluded:

This only accounts for Domestic use of water which include: showing, the toilet, drinking water, etc. This can serve as a guideline when getting a water tank for your home.

There are two other major sectors that attribute to the water consumption in the country namely the Agricultural sector and the Industrial Sector. We delved a bit deeper into the water usage of each sector in a previous post: Steel Water Storage Tanks

But in this post, we will be focussing on the size and capacity of tanks. So let’s start off with some of the most frequent questions:

Does the tank material affect the volume of the water tank?

Yes and no. Let us explain:

The two main water tank materials are Plastic ( Polyethylene ) tanks and Steel tanks.

Plastic tanks have a limit to their size and capacity due to the fact that when they reach a certain size and volume, the pressure when it is filled, becomes too much. Therefore, the plastic water tank can buckle, bend and get damaged because the material is not strong enough to hold that volume.

Steel water tanks have the benefit of not having a capacity and size limit. They can be built to your specifications, as big or small as you require it to be.

Therefore, if you are looking for a smaller tank, the material will have no impact on the size and volume of the tank. However, when you are looking at bigger industrial sand agricultural tanks you might have various limitations when it comes to plastic tanks.

We did some in-depth research on this topic, you can check it out at Steel vs. Plastic water tanks.

Tank Volume Calculator: Cylinder

Lucky for you, we’re going to help you out and direct you to a website that can get the job done for you without using too many calculations. You can head on over to this tank calculator to calculate the volume of the most common tank shapes: Tank Volume Calculator

All you have to do is convert your cm/mm to feet and inches. And the calculator automatically works out the volume for you.

But if you are looking for some serious calculation, fine, we’ll give them to you. To calculate the volume of a cylinder (vertical) in liters, you can use the following formula:

V(fill) = πr2f



You can use the guidelines above to calculate the filled volume of your cylinder.

Important note when you work out the volume of a cylinder-shaped water tank.

  • The total volume of the tank may not necessarily be the fill volume. Some tanks have a max line where the water will fill up, it is important that you use that max fill line value as the “f” in your calculation. 
  • When doing calculations it is important to use cm as your measurements.
  • 1cm/ 1 cm3 = 1ml Therefore, when doing the calculations in cm, you will have to convert your final answer will give you the number of ml the tank will hold. Thereafter, you can convert the ml to liters to get the capacity of your water tank.

Always ask your water tank sales consultant regarding the max capacity of your tank.

Tank Volume Calculator: Square

To calculate the volume of a square tank is relatively straight forward:


To calculate the fill volume of a square, you multiply fill height x length x width.
This formula can also be used for rectangular water tanks.

Few extra notes when calculating the volume of a tank:

  • Remember to use the INSIDE diameter/size measurements of the tank and not the outside.
  • Remember to work in cm, which gives ml answers, then converts it to liters.

Other Tank Shape Volumes

Water Tanks come in many shapes and forms:

  • Cylinder (Vertical and Horizontal)
  • Square
  • Oval
  • Capsule

The square tank and cylinder tanks are the most common types of tanks for domestic and home use. However, if you are looking to calculate the volume of a different water tank, things can get a bit more tricky. You can head on over to Calculator Soup to assist you with those calculations and formulas. They have a handy tank volume calculator (It is in inches and feet, therefore, you will have to convert your cm over to hose measurements before typing the values into the calculator.

How much space will I need for a water tank?

This completely depends on what you are using it for and how many people will be making use of the water inside the tank.

You can take the average amount of water used per day (provided at the beginning of the post, 194 liters), multiply that by the amount of people in your household/business and then multiply it by the number of days you would want the tank’s water to last in the event of a water cut.

Once you have your needed capacity, you can start looking for tanks and their sizes. 

The benefit of steel tanks is that they can be made to your specifications. Therefore, if you have limited space available they can be made in a slimline design to be placed against the wall of your house, next to walkways, etc.

These water tanks can be customized to your heart’s desire, which makes it perfect for any urban areas with limited space.