Bark, soil, gravel and sand are sold by the cubic metre but the garden is measured in square metres. Area times thickness is what turns one into the other, and forgetting the thickness is the classic mistake.
Grass seed
Hedge plants
Paving units
Nothing is filled in for you: layer thickness, sowing rate and planting distance depend on the species, the season and the soil, and they are printed on the bag or in the growers catalogue.