Rain Capture Volume

How to use this calculator

1. Enter roof catchment in m².
2. Enter rainfall in mm.
3. Enter collection efficiency in %.
4. Select Calculate and keep the output unit with the answer.

Before you use the answer

Use measurements from the actual bed, container or watering zone and keep them with a dated garden record. Defaults illustrate arithmetic rather than plant-specific requirements. Soil condition, weather, crop variety and growth stage can change what amount or spacing is appropriate.

This does not assess water quality, plumbing suitability or overflow handling.

Does it save my inputs?

No calculation history is stored by this website. The calculator works locally in your browser. See the privacy policy for hosting and contact details.

Why might a result be approximate?

Measurement uncertainty, ideal-model assumptions and floating-point rounding can all matter. Displaying more digits does not improve the original measurement.