Technical Tool

Rainwater Flow
Specification Tool

Accurately determine the required gutter capacity for your project based on British Standard BS EN 12056-3:2000 Gravity Drainage Systems.

1 Input Dimensions: Enter total area directly OR use length × width for precise calculation.
2 Select Pitch: Steeper roofs drain water faster. Select the appropriate gradient factor.
3 Adjust Downpipes: If the flow exceeds capacity, increase the number of downpipes to split the load.

*Calculations assume a rainfall intensity of 75mm/hr (0.021 L/s/m²). Always verify with a structural engineer for complex geometries.

Project Flow Calculator

Configure your roof parameters below.

Effective Roof Area

150 m²

10 m² 1000 m²

Roof Pitch Factor

Gutter Run Length (m)

Total horizontal length of gutter (one side of building)

Number of Downpipes

Increase this to reduce load per outlet.

Flow Load Per Outlet

0.00 L/s

Total Runoff

0.00 L/s

Calculating...

Adjust parameters above.

Gutter run length: 12.0m

Recommended downpipes: 1

Spacing: Every 12.0m

0m 12.0m

Good spacing

Downpipes are positioned within recommended guidelines.