Measure at the correct height
To determine the diameter of your downpipe, take the measure at the height at which the rainwater filter is to be installed. In this way, you avoid determining an incorrect value for slightly conical downpipes.
Determine the correct diameter
The diameter can be determined directly with the caliper gauge or slide gauge. When measuring, rotate slightly around the downpipe to determine a suitable average value in case teh pie is a little oval. However this method is only suitable for pipe diameters up to about 80 mm. For larger diameters the usual calipers are simply too small.
Measuring the circumference with the tape measure
This method is suitable for all diameters, also for those for which the caliper is too small. Use the tape measure to determine the circumference of the downpipe. The diameter can easily be calculated by dividing the value by the figure Pi, which is 3.14.
Relationship between circumference and diameter
As an example, these circumferences result in approximately the following downpipe diameters: