If gardeners have a clear idea of how to build a gravel bed, the question arises as to the material requirements. A significant cost item in the budget is the required amount of gravel. Anyone who skimps at this point will be annoyed by a patchy gravel cover. However, a calculation that is too generous will unnecessarily increase the costs. This guide explains how to correctly determine how much gravel you need.
How do I calculate the amount of gravel needed for a gravel bed?
To determine the gravel requirement for a gravel bed, multiply length x width x twice the grain height x bulk weight/m³. The optimal dumping height corresponds to twice the grain size of the selected gravel. Also take delivery costs into account or plan the transport yourself.
Grain size defines layer height for opaque gravel covering
General height information for the layer height in the gravel bed only serves as an initial orientation when determining requirements. If you are aiming for an opaque gravel surface, the grain size of your favorite type of gravel comes into focus. Act here according to the following premise:
Rule of thumb: Optimal dumping height corresponds to twice the grain size
If you have chosen white quartz gravel with a grain size of 16-25 mm, apply the gravel at a height of 50 mm, i.e. 0.050 m. Use Donoaus gravel with a grain size of 8-16 mm, the dump height is 32 mm, i.e. 0.032 m.
Formula for material requirements – this is how you calculate correctly
So that you can calculate the amount of gravel you need, first measure the bed. The third piece of information missing for determining requirements is the bulk density per cubic meter of the selected type of gravel. This value is already part of the offer from building material suppliers or can be found on the Internet. The following formula gives you the actual gravel requirement for your bed:
Length x width x double grain height x bulk weight/m³
In order to opaquely cover a 5 m long and 4 m wide bed with Danube gravel 8-16 mm (1.42 t bulk weight per m³), the following calculation results: 5 m x 4 m x 0.032 m x 1420 kg=908, 8 kg gravel requirement.
Include delivery costs
To calculate the costs, first multiply the purchase price per kilogram of gravel by the quantity required. Added to this are the delivery costs, which can be significant given the considerable weight. Savvy home gardeners rent a trailer and drive to the nearest gravel plant.
Tip
So that the calculated amount of gravel stays where it belongs, an adequate bed border is essential. Even a simple metal lawn edge prevents the stones from spreading around the garden. A border made of natural stones sets the scene for the gravel bed decoratively and tastefully.
