Environment calculator
Rainwater Harvesting Calculator
Estimate collectable rainwater from roof area, rainfall, and collection efficiency.
FormulaLiters = roof area sq m x rainfall mm x efficiency
Formula
Rainwater collection
Liters = roof area sq m x rainfall mm x efficiency
100 sq m roof and 50 mm rain at 80% efficiency collects about 4,000 L.
FAQ6 common questions for this calculator.
FAQs
Why does 1 mm of rain equal 1 liter per square meter?+
A 1 mm layer over 1 square meter is 0.001 cubic meters, or 1 liter.
Why include rainwater collection efficiency?+
Gutters, first flush, overflow, evaporation, and roof shape reduce usable collection.
How does the Rainwater Harvesting Calculator calculate the result?+
For the Rainwater Harvesting Calculator, it uses the Rainwater collection: Liters = roof area sq m x rainfall mm x efficiency. 100 sq m roof and 50 mm rain at 80% efficiency collects about 4,000 L.
What information do I need to use the Rainwater Harvesting Calculator?+
For the Rainwater Harvesting Calculator, enter roof area, rainfall, and collection efficiency. Keep the units consistent with the calculator fields and compare your setup with the worked example on the page.
How accurate is the Rainwater Harvesting Calculator?+
Rainwater Harvesting Calculator is accurate for the values and assumptions entered on this page. It uses the Rainwater collection. Recheck the inputs before relying on the estimate.
What should I check before using the Rainwater Harvesting Calculator result?+
For the Rainwater Harvesting Calculator, check that the units, inputs, and assumptions match your situation. Change one input at a time to understand which values have the largest effect on the result.
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Environment guide
How to use the Rainwater Harvesting Calculator
Estimate collectable rainwater from roof area, rainfall, and collection efficiency. The page also explains the rainwater collection and shows a practical example: 100 sq m roof and 50 mm rain at 80% efficiency collects about 4,000 L.
- 1
Enter your details
Enter roof area, rainfall, and collection efficiency, then complete any other fields shown in the calculator.
- 2
Check the calculation
Review the result alongside the rainwater collection: Liters = roof area sq m x rainfall mm x efficiency.
- 3
Compare scenarios
Change one or more inputs to see how they affect the rainwater Harvesting Calculator result before you use the estimate.