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. Depth matters more than people expect. Too shallow and it neither suppresses weeds nor holds moisture; too deep and it suffocates roots and harbours 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:

Four inches is the practical ceiling for a planted bed, and the mulch depth calculator uses the same figures. Past that, water starts running off the surface instead of soaking through, and the layer stays wet against plant crowns. Paths and playgrounds are the exceptions, because nothing is trying to grow up through them.

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 once you are past about two cubic yards. As a rough US guide in 2025, bulk hardwood runs $40–$60 a cubic yard delivered against $4–$8 for a 2 cu ft bag, which is $54–$108 a yard once you have bought enough bags to fill one. Prices move a lot by region and season, so put your own two numbers into the price fields above and let the panel do the comparison properly.

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.