Enter your bed area and how deep you want the mulch, and get the cubic yards and number of bags to buy.
Mulch is measured by volume: the area of your beds times how deep you spread it. Two to four inches is the usual range — 3 inches is a solid default that suppresses weeds and holds moisture without smothering roots. The calculator turns your area and depth into cubic yards (how bulk mulch is sold) and 2-cubic-foot bags (how bagged mulch is sold).
For small beds, bags are convenient. But bulk mulch by the cubic yard is almost always cheaper once you need more than about 10–12 bags — a single cubic yard equals roughly 13½ two-cubic-foot bags. If the calculator shows you need several cubic yards, price out bulk delivery before buying bags.
For a rectangular bed, multiply length by width. For a circular bed, it's π times the radius squared (radius is half the width). For odd shapes, break the bed into rectangles and circles, add them up, and round the total area up a little — mulch settles, and a bit extra is better than a bare patch.
About 13.5 bags if they're 2 cubic feet each (27 cubic feet make a cubic yard). Once you need more than roughly 10–12 bags, bulk delivery is usually cheaper.
Two to four inches for most beds; three inches is a good default. Deeper than four can suffocate roots and hold too much moisture against stems.
Break it into rectangles and circles, calculate each area, and add them up. Rectangle is length × width; circle is π × radius². Round the total up slightly for settling.