For most applications in residential landscaping, 75mm (3") is sufficient for Mulching beds. The first task is to find out the area of your shrub bed (in square feet). To do this multiply the length and the width of the bed. Then take the area of the bed and divide by 100. This will give you the amount of Mulch (cubic yards) you will need to cover your shrub bed with a 75mm (3") depth of Mulch.
Come visit us at Classic Landscapes and see our wide selection of rock Mulches, as well as wood Mulches!