Roof Rainwater Collection Calculator

How much rainfall can you harvest in your area?

It's simple to calculate how much rainfall you can harvest from any roof size even accounting for loss. Simply enter a few basic measurements into our rainfall calculator.

Rainfall Calculator

roof rainwater collection calculator

How to Use

  1. Roof area: select whether you already know your roof's total area. If not, provide the width and height of your roof.
  2. Select the unit of measurement: choose between square meters or square feet.
  3. Enter your roof area, width, or height: the calculator assumes a rectangular shape for simplicity.
  4. Select the rainfall measurement unit: millimeters or inches.
  5. Average annual rainfall: Enter the amount of rainfall your area receives.
  6. Calculate your rainwater amount: click the "Calculate" button to show the total potential rainwater collection for a year, followed by the estimated collection considering an 80% efficiency rate.

Calculator checked on By Jamie

Annual Rainfall

Don't know the annual rainfall in your area? Visit the USA.com website.

80% Efficiency

Due to small amounts of rainfall that don't generate runoff, evaporation, and small filtering losses you should realistically expect an 80% rainwater collection efficiency.

Uses

  • Home Rainwater Harvesting: estimate how much rainwater you can collect for use in gardening, toilet flushing, and other non-potable purposes.
  • Agricultural Planning: calculate potential rainwater collection from farm buildings or greenhouses to supplement irrigation needs.
  • Sustainable Design: incorporate rainwater harvesting calculations into sustainable building designs.
  • Urban Planning: estimate collection potential for public buildings, parks, and other urban surfaces to manage stormwater and reduce runoff.
  • Water Conservation Projects: plan and promote water conservation projects, encouraging rainwater harvesting as a sustainable practice.
  • Cost-Benefit Analysis: compare the potential savings on water bills against the investment in harvesting equipment.