Water Runoff Reduction Calculator
Estimate how much stormwater runoff is cut by swapping hard surface for permeable or green surface.
Compare Your Options And Get Clear Answers
Estimate how much stormwater runoff is cut by swapping hard surface for permeable or green surface.
Water Runoff Reduction Estimator
Enter your numbers below for an instant estimate.
How It Works
Key concepts behind this calculator
Enter Values
Fill in each field with your own numbers.
Calculate
Results update as you change the inputs.
Review
Read the breakdown and the explanation.
Adjust
Change values to compare scenarios.
Water Quick Guide
Typical values for reference.
| Area m2 | Rain mm | C before | Saved L |
|---|---|---|---|
| 50 | 25 | 0.9 | 625 litres |
| 200 | 25 | 0.9 | 2,500 litres |
| 500 | 25 | 0.9 | 6,250 litres |
| 1000 | 40 | 0.9 | 20,000 litres |
| Rule of Thumb | Check inputs | Use as a guide | Round sensibly |
Water Runoff Reduction Calculator FAQ
Answers to common questions about this calculator.
The share of rain that runs off a surface, from 0 to 1.
Permeable paving, green roofs, rain gardens and water butts.
Runoff = area x rainfall x runoff coefficient; reduction = before – after.
It is an estimate based on the inputs you enter. Check real quotes, labels or official guidance for important decisions.