Rain Inside a Flood Wall: Volume and Pump Size

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Opens on the book's own wall. Change any number to your own and press Calculate.

Yard inside the wall: length m

width m

Roof that drains inside m²

Storm

Storm in

Hours it lasts

Pump capacity at your lift US gal per hour

Enter the area and the storm, then press Calculate.

From the book, Chapter 7. The book's yard is 8.4 × 3.2 m with 40 m² of roof draining into it: 66.88 m². A 50 mm hour of rain puts 3.344 m³ (883 US gallons) inside the wall, and a pump rated 2,400 gal an hour at 10 ft lift handles it 2.7 times over.

FEMA says a flood wall needs an interior drainage system with a sump pump, and backup power. Use your local design storm (in the US, NOAA Atlas 14) and the pump's rating at your real lift. Prices are illustrative US home-center prices from October 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.