Roof catchment planning

Rainwater Harvesting Capacity Calculator

Estimate harvestable rainwater from roof area, rainfall and collection efficiency, then compare storage and monthly demand.

Enter your values

Example values demonstrate the method; they are not product recommendations.

Your result

Enter measured or nameplate values to calculate.

Method

One millimetre of rain over one square metre equals one litre before losses. Harvest = roof area × rainfall × entered collection efficiency.

Important limits

Period totals do not model storm timing, first flush, water quality, treatment, plumbing, local rules or dry-season reliability. Use monthly or daily data for storage design.

Technical reference