Rainwater tank calculatorPro
See how much rain your roof can collect in a year and how many days of water a tank holds.
Your measurements
How it's worked out
Litres per year = roof area (m²) × annual rainfall (mm) × runoff factor (0.9 for metal, 0.8 for tiles). Days of supply = tank size ÷ daily use. Find your annual rainfall on the Bureau of Meteorology website.
Estimates only. Check sizes, coverage and quantities with your supplier, engineer or certifier before ordering. Standards references are a guide, not compliance advice.
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