Rainwater Calculator
See how much rainwater you could collect
How Much?
If you are planning a rainwater harvesting system UK, one of the first questions is simple: how much water could your building actually collect?
What Is It?
This tool gives you a quick estimate based on your roof area and local rainfall. It is a useful starting point if you are exploring a new system or comparing rainwater harvesting tanks.
Plan Ahead
Rainwater can be collected from many types of buildings, including homes, offices, warehouses, restaurants, agricultural sheds and industrial units. The amount you can collect depends mainly on the size of your roof and the rainfall in your area.
How the calculator works
The calculation is based on a simple formula:
Roof area (m²) × annual rainfall = potential rainwater collection
Our current guidance also suggests dividing the annual figure by 12 to estimate average monthly rainfall capture.
This is an initial guide only, but it can help you begin thinking about:
-
how much water you may be able to collect
-
what size rainwater tank may be suitable
-
whether above-ground or below-ground storage may work better
-
how much stored water you may want to keep available on site
