Mulch Calculator Let’s figure out how much mulch or material you need: How many square feet do you have? Square or Rectangle Length (feet) Width (feet) Area (Square feet): How thick do you want the mulch? 1″2″3″4″How big is your garden/bed (sq. ft.): You will need: 2-cubic-foot bags or 3-cubic-foot bags or cubic feet or cubic yards or pickup truck loads (midsize)