Capacity Table for Common Size Downpipes

The capacity of a downpipe is nearly always governed by the capacity of the dropper. As droppers fit inside the downpipe, their inside diameter will be less and varies by manufacturer.

The figures allowed for in our calculator are the smallest dropper internal diameter measured from commonly available products. For the 65mm diameter downpipe, the smallest dropper measured was one with squared sides to fit in either 65mm round or 65 x 50 rectangular downpipe.

Use this table to select the correct internal dimensions of common downpipe sizes. The Downpipe Capacity Calculator will use these values to perform the correct calculations without the need to enter them manually.