How this mulch calculator works
The calculator turns a flat measurement into a volume you can order. Mulch is sold by the cubic yard in bulk, and in bags at retail. Volume is what you buy, so the tool converts your bed dimensions into cubic yards and bag counts.
Start with the area you want to cover. For a rectangle, multiply length by width in feet to get square feet. For an odd shape, break it into rectangles and circles, then add the pieces. Enter that total area.
Next, set the depth. You measure and enter depth in inches, because that is how mulch is applied. The tool converts inches to feet by dividing by 12. It then multiplies area by depth in feet to get cubic feet.
The last steps convert cubic feet into buying units. Dividing cubic feet by 27 gives cubic yards, since one cubic yard equals 27 cubic feet. Dividing cubic feet by 2 gives the bag count, because a standard retail bag holds 2 cubic feet.
The calculator also adds an overage allowance on top of the raw volume. The default is 10%, and you can change it. This covers settling and small measuring errors, which are covered in a later section. The result is a cubic-yard figure for bulk and a bag figure for bagged mulch, so you can compare the two ways to buy.