Rainwater Collection Calculator
Litres collected from your roof.
Enter your values
ⓘ Live results
Results
- Water collected
- 3,060 litres
- In gallons
- 808
- Days of supply
- 51
- Annual estimate (×12)
- 36,720 litres
Quick answer
One millimetre of rain on one square metre of roof yields one litre of water.
Litres = area × rainfall × efficiency
How to use the Rainwater Collection Calculator
- 1Enter your roof's plan area.
- 2Enter rainfall for the period.
- 3Adjust efficiency for gutter and filter losses.
Worked example
Using the values the calculator loads with:
Inputs
- Roof area80 m²
- Rainfall45 mm
- Collection efficiency85 %
- Daily water use60 L
Results
- Water collected3,060 litres
- In gallons808
- Days of supply51
- Annual estimate (×12)36,720 litres
Frequently asked questions
Is roof area the sloped area?
No — use the flat footprint area for rainfall capture.
Is rainwater drinkable?
Not without proper filtration and treatment.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.