Rainwater Tank Size Calculator
Answer a few questions about your roof, rainfall and water usage. We'll calculate the right tank size and recommend the best system for your project.
1
Roof & Rainfall
Total roof area that drains into your system
Irish average is ~1200 l/m²/year — adjust for your county
2
Water Usage
Number of people in the household
For garden-only use, leave both unchecked.
Leave blank if not using for garden irrigation
12 l/person/day
6 l/person/day
2 l/person/day
200 l/m²/year
250 l/m²/year
3
Dry Period Bridging
How many days should the tank cover during a dry spell? 20 days is the standard per the GRAF sizing sheet.
Rainwater Yield
—
litres / year
Total Water Demand
—
litres / year
Recommended Storage Volume
—
litres — based on 30-day dry period
⚠️ Your rainwater yield is less than your water demand. You may want to connect additional roof areas to increase collection.
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