How Rainwater Harvesting Calculator Works
Estimate rainwater collection from roof area, rainfall and collection efficiency. The calculation runs locally in your browser, so values entered into this calculator are not sent to a server by the calculator.
Roof area × rainfall × collection efficiency gives estimated collected water. Rainfall is converted from mm to metres.
How to use it
- Measure or verify each input and use the units shown.
- Run the calculation and compare alternative assumptions when planning quantities or capacity.
- Allow for waste, tolerances, access space, installation conditions and local requirements where applicable.
- For safety-critical work, verify the result with the applicable standard, manufacturer guidance or a qualified professional.
Common mistakes
- Mixing metric units or entering a dimension in the wrong unit.
- Using nominal dimensions when usable dimensions are required.
- Ignoring efficiency, waste, density or spacing assumptions.
- Treating an estimate as a final design, compliance certificate or safety approval.
Limitations
This calculator provides a preliminary mathematical estimate. Real-world results can vary because of material properties, installation conditions, tolerances, environmental factors, local standards and supplier specifications.