Water Tank Sizes Calculator

Pioneer Water Tanks - Water Tank Size Calculator

What Size Water Tank Do I Need?

Water tanks are a significant investment for many people, and one thing they want to be sure of is that they purchase the absolute best water tank size to suit their needs now and into the future.

Pioneer Water Tanks have made a name providing Australian-made tanks to families and farmers across WA for more than 3 years, and know that information is power when it comes to calculations like these.

While there is no clear-cut answer to what size rainwater tank is best for your home, Pioneer Water Tanks have put together a range of calculators to help you figure out your rainwater harvesting capacity and what size tank you need.

As well as that, we have included a tank volume calculator to determine the volume of any cylinder tank you may be trying to calculate the capacity of.

There are a range of measurements regarding shapes and dimensions you may need to use these calculators, and they are designed for large round tanks. For a rectangular or oval tank, you will need to use a calculator specific to that shape.


Pioneer Water Tanks have provided a service for Western Australia since 1988. Our high quality Australian-made water tanks will provide the long-term water security you’re looking for.

Calculate Your Potential Water Supply

To determine how much rainwater you can harvest from your roof (catchment area) use the simple calculator below:

To get the most accurate calculation it is best to factor in your total rainfall harvesting area (total roof of the home, and any sheds with gutters you will be harvesting from), as well as using rainfall figures local to your property’s microclimate where possible, rather than general data from your region.

Rainwater Tank Size Calculator

Use the calculator below to calculate the water tank size best for you

NOTE: The tank sizes displayed here are simply recommendations, and each family will have different water storage needs based on climate, appliances and property water usage.

Water Tank Calculator

Calculate water tank sizes Australia

In order to use this calculator’s formula, you will need the radius (width of your rainwater tank at its widest interior point), and the vertical height of your tank (from the ground to the top of the wall, not the highest point of the roof)

If you can’t measure the internal radius, measure the total length of your tank’s diameter, halve it, and then minus the thickness of your tank wall.

NOTE: Result here will be an estimate only, and actual tank capacity will differ based on factors such as liner thickness and outlet height, as well as exact cm used.

Calculate the size of your Pioneer Water Tank

Without taking a diameter measurement, you can calculate the size of a Pioneer Water Tank from the number of bolt strips covers around the outside of the tank. 

A table indicating Pioneer Water Tanks sizes to determine them from the number of bolt strip covers on the tank

Water Tank Sizes and Capacity

Water Tank Size Chart

Pioneer Water Tanks have a range of steel water tanks available, that are designed for above ground residential, commercial or industrial use. The water tank sizes listed below all include Pioneer’s standard range of water tank accessories.

pioneer water tank sizes and dimensions

The Litres/Gallons stated above are gross capacities. Actual useable volume will vary depending on the size and position of inlets and outlets.

Volume of products required for tank construction

There are other important materials to have prepared for your water tank installation, which you may also want to calculate the amount required. These include the clean sand required for a level sand pad, the aggregate required to prevent erosion, and the liquid required to fill the tank after installation so that has sufficient weight.

A table of Pioneer Water Tank sizes and the amount of water, sand and aggregate required for before and after building

Have questions regarding the best water tank size for your home?

If you’re looking for more information on the best water tank size for your home, give us a call on 1800 999 599, or simply click here to request a quote from one of our experienced water tank dealers. 

Frequently Asked Questions

How do I calculate what size water tank I need?

There are a number of factors to take into consideration when calculating what size tank you need. First it is important to know how much water your family uses each year (can calculate monthly and multiply by 12). You also want to know how much rainwater you can harvest from your home, as well as how much space you have to install a water tank.

Once you have all of these figures, you will be able to calculate a clearer image of what size water tank you need.

How do you calculate the m³ of a tank?

Calculating the gross volume of a tank is a simple equation. You need the radius (half the internal diameter) and the height of the tank wall. The gross volume will be equal to r² x h x π.

For a Pioneer GT 90, this would look like this: ((367 x 367) x 218 x 3.14)  = (92 197 314ml / 1000) = 92 197L.

As the gross capacity of a GT90 is calculated at 92 570L, this fluctuation is likely due to the exact cm not being present, combined with not using the exact numbers of pi, but gets you close enough to your desired number.

This is for cylinders only. For other tank shapes, be it a cube, sphere or prism, you’re going to need the right formula for your needs.

How much water does a family of 4 use per day Australia?

This figure is different for rural homes to suburban homes, as people in cities or suburbs often use more water annually than people located in rural or country parts of Australia. For example, some estimates indicate that people in the suburbs use 100,000L of water per year, while Pioneer Water Tanks estimates you will need approximately 30,000 litres of water storage, plus an additional 30,000 litres per person in the home.

What size of tank do you offer?

Pioneer Water Tanks offers a range of water tank sizes from 12,000 litres all the way up to 500,000 litres, and these tanks can be joined together if required to reach your ideal water storage setup. These sizes are broken up into 22 different size units, in order to help you more accurately meet your water storage needs.

How many litres is a full tank?

The litres listed as your water tank’s gross capacity will be the total volume of the cylinder itself, and won’t take into consideration the location of any overflow or outlet valves which will impact the overall operating capacity of your rainwater tank. This is why it is better to err on the side of a larger tank than a smaller one.