How to use the Mulch Calculator
- Enter the length and width of each bed, or the total area.
- Enter the desired depth in inches.
- Read the volume in cubic feet, cubic yards and bags.
- Compare bulk delivery cost against the bagged equivalent.
How the calculation works
Volume in cubic feet = area in square feet × depth in inches ÷ 12. One cubic yard is 27 cubic feet, so one yard covers 108 square feet at 3 inches or 162 square feet at 2 inches. Standard bags hold 2 cubic feet, meaning 13.5 bags per cubic yard — the point where bulk delivery usually becomes cheaper is around three cubic yards, once delivery fees are spread.
Depth guidance matters more than volume precision. Two to three inches is right for most beds; below two inches weeds break through, and above four inches around trees or shrubs the mulch holds moisture against the bark and invites rot. Never pile mulch against a trunk — leave a gap and keep the root flare exposed. Organic mulches settle and decompose by roughly a third in the first year, so annual topping-up needs about a third of the original volume rather than a full replacement. For irregular beds, break the shape into rectangles and part-circles and sum the areas.
Cubic yards = area (sq ft) × depth (in) / 324 ; bags = cubic yards × 13.5 for 2 cu ft bagsSource: Standard bulk landscape material volume conversion: 27 cu ft per cubic yard.
Worked example
Beds totalling 640 square feet at 3 inches deep.
- Cubic feet = 640 × 3 / 12 = 160.
- Cubic yards = 160 / 27 = 5.93.
- Round up to 6 cubic yards for delivery.
- Bagged equivalent = 80 two-cubic-foot bags.
About 6 cubic yards, or 80 bags — bulk delivery is clearly cheaper at this volume.
Frequently asked questions
How deep should mulch be?+
Two to three inches for most beds. Thinner lets weeds through; much thicker risks rot at the stem.
How many bags in a cubic yard?+
13.5 two-cubic-foot bags, or 9 three-cubic-foot bags.
When is bulk cheaper than bags?+
Usually from about three cubic yards, once delivery is spread across the volume.
How much do I need each year after the first?+
Roughly a third of the original volume, since organic mulch decomposes and settles.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.