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
How to Use
- Roof area: select whether you already know your roof's total area. If not, provide the width and height of your roof.
- Select the unit of measurement: choose between square metres or square feet.
- Enter your roof area, width, or height: the calculator assumes a rectangular shape for simplicity.
- Select the rainfall measurement unit: millimetres or inches.
- Average annual rainfall: Enter the amount of rainfall your area receives.
- 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 Met Office 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.
More Measurement Calculators
Batten Spacing
Rafter Length
Rainwater Collection
Roof Slope
Roof Tarp Size
Truss Count