Calculating volumes

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Calculating volumes

We often need to calculate volumes of regular and irregular shapes to help estimate how much top dressing, mulch or soil we may need for different jobs.

Regular shapes

The volume of a regular shape can be calculated using the formula:

Volume = length x breadth x height

For example:

To top dress a bowling green measuring 40 metres by 40 metres to a depth of five millimetres

Volume = length x breadth x height

= 40 x 40 x 0.005

= 1600 x 0.005

= 8 cubic metres

Circular shapes use a different formula:

Volume = r² x height

For example:

To excavate a circular golf green with a radius of 15 metres to a depth of five centimetres

Volume = r² x height

= 3.14 x 15 x 15 x 0.05

= 35.325 cubic metres

Sometimes it's necessary to estimate volumes of irregular areas such as kidney-shaped garden beds or hourglass greens.

Irregular shapes

The key to measuring the volume of these shapes is to calculate an average radius and then apply the formula for circular shapes.

For example:

To excavate a kidney-shaped green to a depth of five centimetres, first calculate an average radius. This is done by measuring from a central point (not necessarily the exact centre) of the green to the edge of the green at ten degree intervals.

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Total all the measurements and then divide by the number of measurements to give an average radius. This can then be used in the standard formula:

Volume = r² x height

If the average radius was 15 metres then:

= 3.14 x 15 x 15 x 0.05

= 35.325 cubic metres

If you are trying to estimate the volume of soil or turf being taken out of an area then you will need to allow about ten per cent for decompaction (i.e. once soil is broken up and disturbed it will take up more space than it does in the ground).

Conversely, when estimating the volume of soil to be added to a site, allow 30 per cent for compaction to accommodate the soil settling and compacting down.