How we got these numbers
Enter roof, rainfall, and demand to see the step-by-step.
Formulas
- Gross volume (US) = area(ft²) × rain(in) × 0.623
- Gross volume (metric shortcut) = area(m²) × rain(mm) (liters)
- Harvestable = gross × runoff coefficient − first-flush (≥ 0)
- Suggested tank = daily demand × desired days
- Days from harvest = harvestable ÷ daily demand
- Days from existing tank = tank ÷ daily demand
Prepared by AgCalculator · Estimates only · Verify with local code and water quality guidance for potable uses.