How to use the rainwater harvesting yield calculator
Estimate how much water a roof can collect in a year from its area, rainfall and runoff efficiency. Enter roof catchment area, annual rainfall, runoff coefficient in the fields above; the harvested water per year are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “rainwater harvesting calculator”, “roof water collection”, “litres of rain per year”, “calculate rainwater harvesting yield”, “find harvested water per year”.
Formula
Variables
- area — Roof catchment area (m²)
- rain — Annual rainfall (mm)
- cf — Runoff coefficient
Worked example
With roof catchment area = 100 m², annual rainfall = 800 mm, runoff coefficient = 0.8, the calculator gives harvested water per year ≈ 64,000 litres; harvested water per year ≈ 64 m³.
Frequently asked questions
What is the rainwater harvesting yield calculator used for?
Estimate how much water a roof can collect in a year from its area, rainfall and runoff efficiency. It helps with questions such as “rainwater harvesting calculator”, “roof water collection”, “litres of rain per year”.
What is the formula for the rainwater harvesting yield calculation?
Harvested water per year (litres) = area × rain × cf. Harvested water per year (m³) = [Harvested water per year] / 1000. Here area is roof catchment area (m²), rain is annual rainfall (mm), cf is runoff coefficient.
What inputs do I need for the rainwater harvesting yield calculator?
You need roof catchment area in m², annual rainfall in mm, runoff coefficient. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the rainwater harvesting yield calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the rainwater harvesting yield result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.