Gutters and drains come in different sizes. The right size for your roof depends on the roof footprint and the number of drains.
Example for the calculation of the reference values
The gable roof of a house with a length of 15 m and a width of 10 m is to be drained. The floor area of the house is therefore 150 m². If each side of the house receives a downpipe connection, the floor area to be drained is 75 m². As you can see from the table, you need a Marley RG 125 gutter and a Marley DN 105 downpipe on each side for this house. If you connect two drains on each side of the house, the floor area to be drained is halved to 37.5 m². As shown in the table, you can now install one Marley RG 100 gutter and two Marley DN 75 downspouts on each side.