Mulch Coverage by Depth: Cubic Yard and Bag Table

Coverage comes from volume divided by depth

Coverage in square feet equals volume in cubic feet × 12 ÷ depth in inches. The table describes geometry only; it is not a recommendation to use each depth.

Example: topping up an existing bed

Suppose a 12 × 18 ft bed requires an additional 2-inch layer. The added volume is 216 × 2 ÷ 12 = 36 ft³, or 1.333 yd³. Without a purchase allowance, that is eighteen 2 ft³ bags. Do not use the total desired depth if some suitable material is already present.

Keep measurement and horticulture separate

Depth changes both quantity and growing conditions. The right choice depends on plantings, existing material, and the mulch itself. Measure several points where the bed is uneven, then choose an explicit allowance for uncertainty instead of silently increasing all dimensions.

• Exclude surfaces that will remain uncovered.
• Avoid counting existing material as a new purchase.
• Check appropriate depth with planting guidance rather than this conversion table.

Sources and product references

• University of Minnesota Extension — mulching

  Organic and inorganic mulch behavior; application depth depends on the landscape.

• NIST — SI units: volume

  Unit relationships; supplier product coverage and prices remain separate inputs.