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About this calculator

Enter Roof area (m2) and the Rainwater Harvest calculates Rain 10 mm, Rain 25 mm, Rain 50 mm in one step. It is built for home & construction jobs where a quick, repeatable answer beats guesswork. Real rain collected depends on runoff, gutter losses and first flush; plan on 80 to 90%.

How it works

The calculator multiplies your input by a fixed coefficient for each line. For example, every 1 m2 gives 10 L for rain 10 mm.

Worked example

If you enter 75 (Roof area (m2)), Rain 10 mm comes to 750 L and Rain 50 mm comes to 3,750 L.

Common mistakes

• Real rain collected depends on runoff, gutter losses and first flush; plan on 80 to 90%.
• Mixing metric and imperial measurements on the same job.

FAQ

How much rain 10 mm do I need per m2?

Each 1 m2 gives 10 L.

How is Rain 50 mm calculated?

Rain 50 mm equals your input times 50 L. With 75 entered, that is 3,750 L.

Are the results exact?

Multiplication is exact; the inputs behind rain 10 mm are typical figures, so check them against your own conditions. This is general information, not professional advice.

What is the most common mistake?

Real rain collected depends on runoff, gutter losses and first flush; plan on 80 to 90%.

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