To do in your head and make it easy.
Round down the yards to 25 cubic feet and use 3 inches or .25
so to make it easy
17 yards will give you between 3 to 4 inches if you are correct at the 1700 sf.
This will get you with in 15% of the 4" calculation but you also assume you have plant material in existing beds and do not pile up mulch on the base of the shrub.