Estimate the cubic yards and bags of mulch your beds need. Each dimension has its own unit selector (in/ft/yd/m).
Measure each bed and find its volume (length x width x depth), divide by 27 for cubic yards. A 3-inch layer is typical. Bagged mulch comes in 1.5, 2 or 3 cubic-foot bags - use the bag preset, and divide the total cubic feet by the bag size for the number of bags. Switch any field's unit as needed.