Cracker dust can be installed at a depth of 50-100mm.

Cracker dust is sold in cubic metres. Use the equation square metres x cracker dust depth to calculate how many cubic metres you may need, For example, and area that is 4metres x 5metres will be 20 square metres in size. If installing cracker dust to a depth of 70mm, use the equation 20 square metres x 0.07 to determine the cubic metre amount.

Alternatively, use a soil calculator, such as this one from Soils aint Soils.