Mulch Calculator

Mulch quantity calculation determines how many cubic yards or bags of mulch you need to cover a garden bed to a specified depth. Proper mulch depth is critical — too shallow fails to suppress weeds and retain moisture; too deep can suffocate plant roots and harbor pests.

Core formula: Volume (cubic feet) = Area (sq ft) × Depth (ft) Volume (cubic yards) = Volume (cubic feet) ÷ 27 Bags needed = Volume (cubic feet) ÷ Bag Size (cubic feet)

Note: Depth must be in feet (divide inches by 12 before calculating).

What each variable means:

• Area: the square footage of the garden bed to be mulched. For irregular shapes, break into rectangles and sum, or use length × width for a conservative estimate.
• Depth: desired mulch layer thickness. The recommended depth depends on mulch type and purpose.
• Cubic yards: the standard unit for bulk mulch delivered by truck. 1 cubic yard = 27 cubic feet.
• Bag size: bagged mulch is sold in 2 cubic foot bags (most common) or 3 cubic foot bags at home improvement stores.

Recommended mulch depths by purpose:

Mulch types and coverage:

• Shredded hardwood bark: most common, lasts 2–3 years, good weed suppression
• Pine bark nuggets: decorative, slower to decompose, poor weed suppression
• Cedar mulch: natural pest deterrent, lasts 3–5 years
• Rubber mulch: extremely long-lasting (10+ years), used for playgrounds
• Straw: lightweight, best for vegetable gardens, breaks down quickly

Worked example: Garden bed: 15 ft × 20 ft = 300 sq ft. Desired depth: 3 inches = 0.25 ft.

Volume = 300 × 0.25 = 75 cubic feet Cubic yards = 75 ÷ 27 = 2.78 cubic yards (order 3 yards) Bagged (2 cu ft bags) = 75 ÷ 2 = 37.5 bags (buy 38 bags)

Bulk delivery is almost always cheaper for areas over 250 sq ft. At $40–$60/cubic yard delivered vs. $6–$8 per 2 cu ft bag ($3–$4/cu ft), bulk saves 25–50%.

Don’t volcano-mulch your trees

The biggest mistake in residential mulching is piling mulch in a cone against tree trunks (“volcano mulching”). Mulch touching bark traps moisture against the trunk, attracts boring insects, and encourages rot at the root flare. The right shape is a flat doughnut: keep mulch 3–4 inches away from the trunk on all sides, taper down toward the trunk, and never let mulch touch the bark itself. The root flare (where the trunk meets the roots) should be visible. Trees that have been volcano-mulched for years often die slowly from the inside out, with the homeowner never connecting cause and effect.