How to use this calculator
Estimate roof runoff capture from a rainfall event. Enter catchment area (m²), rainfall (mm), collection efficiency (%). The result updates when you change an input. To compare two sets of inputs, save scenario A, then enter the second set; the result panel shows the difference.
Formula and limits
Liters collected = area(m²) × rain(mm) × efficiency/100. Assumes uniform rainfall; excludes storage overflow and water-quality considerations.
Worked example
The following example uses the calculator’s starting values. It is an illustration of the method, not a recommended target.
| Input | Example value |
|---|---|
| Catchment area (m²) | 100 |
| Rainfall (mm) | 20 |
| Collection efficiency (%) | 80 |
Estimated liters collected: 1,600
Interpreting your result
Enter local prices, equipment ratings, and emissions factors where required. Sample factors are illustrative. Real usage, weather, and equipment efficiency can change the result.
Comparing alternatives
Save the first result as scenario A, then change one input. The comparison shows the numeric difference; it does not label either result as better. Choose inputs that describe realistic alternatives. Values shown on screen are rounded, so calculations from rounded intermediate results may differ slightly.