What is Rainwater Harvesting Calculator?
Rainwater Harvesting Calculator helps you estimate collectable rainwater from roof area, rainfall and collection efficiency.
The main result is collectable rainwater, with a breakdown of collectable volume. The formula, example and assumptions below explain how to interpret it.
How to use Rainwater Harvesting Calculator
Use the example to get familiar with the form, then enter your own figures. Any rates in the example are illustrative. Check the field labels and units before calculating.
- Gather catchment / roof area (m²), rainfall during period (mm) and collection / runoff efficiency (%). Use values from the same situation or reporting period.
- Replace the example catchment / roof area with your own value, then complete the other fields. Check the displayed units.
- Select Calculate and read collectable rainwater with its result breakdown. Change one input and calculate again to compare a second scenario. Reset restores the original example.
- Enter catchment / roof area in m², at least 0. Decimals are accepted.
- Enter rainfall during period in mm, at least 0. Decimals are accepted.
- Enter collection / runoff efficiency in %, at least 0 and at most 100. Decimals are accepted.
Rainwater Harvesting Calculator: a worked example
With the inputs below, the result is 64,000 litres (collectable rainwater). Follow the example, then replace these illustrative values with your own.
| Input or output | Example value |
|---|---|
| Catchment / roof area (m²) | 100 m² |
| Rainfall during period (mm) | 800 mm |
| Collection / runoff efficiency (%) | 80 % |
| Collectable rainwater | 64,000 litres |
| Collectable volume | 64 m³ |
Understanding the Rainwater Harvesting result
Read collectable rainwater alongside collectable volume. These describe different parts of the same calculation.
Displayed results use a readable number of decimal places. When checking a result by hand, keep extra precision until the last step. To compare scenarios, change one input at a time and keep the others fixed.
- Example Collectable volume: 64 m³
Rainwater Harvesting Calculator: assumptions and common mistakes
A useful estimate starts with the right inputs. Check the following assumptions and limits before applying the result to your situation.
- Match factors to your location and reporting period. A result covers the sources you entered, not an independently verified full footprint.
For wider guidance, visit GHG Protocol calculation guidance. The formula and scope of this specific tool are stated on this page.
