How to Use the Rainwater Harvesting Calculator

  1. Roof Area: Measure the section of your roof where you plan to collect rainwater and enter the size in square feet.
  2. Rainfall: Find the average rainfall for your area (check weather services) and input the amount in inches.
  3. Efficiency: Estimate how much rain your roof can capture.
    • Metal roofs are most efficient; tile/concrete are mid-range, and asphalt shingles least efficient.
  4. Click 'Calculate': Get an estimate of the potential rainwater you can collect!


  • Consider water storage capacity when planning how to use harvested rainwater.
  • Check local regulations about rainwater harvesting.

How Much Water Can You Save?