Tank Size Calculator

The most suitable tank size can be determined with a few simple calculations and considerations. Below is a basic guide, however for more info please feel free to contact us to discuss your options.

How To Size Your Tank

Factors To Consider

Things you need to consider when determining the size of your tank(s) include:
1. Rainfall - how much rainfall you get in your area.
2. Roof area - how large the catchment surface is.
3. Water usage - what you intend to use rainwater for, and how much you expect to use.
4. Site characteristics - how much space you have, and the location you intend to install the tank.
Rain Water Tank Volume Map

1) Rainfall

To determine your local rainfall:
- View a rainfall map on the Bureau of Metereology (BOM) website (click on your state/territory for finer detail).
- View exact rainfall figures from your nearest weather station- Bureau of Metereology (BOM).

2) Roof Catchment Capacity

Formula: Roof Area X Annual Rainfall = Total Roof Catchment Capacity
Eg: 200m2 X 350mm = 70,000 Ltrs
Simple rule of thumb for recommended tank capacity; divide the above by 2 = 35,000 Ltrs

3) Water Usage

To determine volume based on water usage:
Most Days without Rain X Average Daily Water Use = Storage Volume Required on Day One of a Dry Spell
Example, if the most days without rain was 40 days, and the average daily usage was 400L, the volume required on Day One of 40 days would need to be 16,000Ltrs.
If you don’t want to catch the maximum available water to collect, then your tank size decision would be based on other factors. Note- people use 1-200Ltrs of water per day.

4) Site Characteristics

Lastly determine where the tank will be located and how much space is available. We have a range of tank sizes that may suit your property. Alternatively ask us about custom sizes.

Further Resources

The Tankulator is a useful and detailed online calculator http://tankulator.ata.org.au
Your Home provides a very useful resource on tanks and related information.