Formula
Volume = area × depthCubic yards = cubic feet ÷ 27Bags = volume ÷ bag size, rounded up How it works
Multiply the bed’s area by the depth you want, keeping the units consistent. 200 ft² at 3 inches deep is 200 × 0.25 = 50 ft³, which is 1.85 cubic yards or 25 two-cubic-foot bags.
Two to three inches of mulch suppresses weeds and holds moisture without smothering roots; topping up an existing layer usually needs only an inch. Keep mulch a few inches away from tree trunks and plant stems to prevent rot.
Bulk mulch is sold by the cubic yard and is typically much cheaper per yard than bags once you need more than two or three yards. The same calculation works for compost, topsoil and decorative bark.
Frequently asked questions
How many bags of mulch are in a cubic yard?
13.5 two-cubic-foot bags, or 9 three-cubic-foot bags, since a cubic yard is 27 ft³.
How do I measure an irregular bed?
Approximate it with rectangles and circles, or walk it with a measuring wheel. Being within 10% is fine for mulch.