Instructions for the use of these calculators will appear in a panel to the right of the screen.

It is important that these instructions are followed in sequence.


Use the [Tab] key to progress through the calculation process


Two Calculators are available


Gutter Calculator

This will calculate capacities for an eaves gutter to BSEN 12056 Part 3.

For the gutter calculator click here.


Flat Roof Calculator

This will calculate the size of chutes and hoppers draining from a flat roof to downpipes on the exterior of the building to BSEN 12056 Part 3. The design assumes a 50 year building life with a 1.5 safety factor. For other design conditions please send details about your project to Guttermaster so that calculations can be performed for you.

For the flat roof calculator click here.