Mulch Calculator — Cubic Yards & Bags Needed

How to use this mulch calculator

Enter the length and width of your garden bed in feet, then the depth in inches. The calculator returns cubic yards (how bulk mulch is sold), cubic feet, the number of standard 2 cubic foot bags, and tons for reference.

For irregular beds, break them into rectangles and add the results. For circular beds around trees, use π × radius² × depth (feet) ÷ 27 for cubic yards. Most beds need less mulch than homeowners guess — it's surprisingly easy to over-order.

Recommended mulch depth

Getting depth right matters more than choosing the "right" mulch type. Most beds need less depth than homeowners instinctively add:

• Flower beds and annuals: 2–3 inches
• Shrub and perennial beds: 3–4 inches
• Around trees: 3–4 inches (NEVER against the trunk)
• Vegetable gardens: 2–3 inches, preferably straw or leaves
• Topping up existing mulch: 1–2 inches to refresh
• Pathways: 3–4 inches, wood chips or bark

Too deep is worse than too shallow. More than 4 inches of mulch can suffocate roots, create a haven for pests, and cause "mulch volcanoes" around trees that rot the trunk. The 2017 Purdue extension data on mulch-related tree death identified volcano mulching as a leading cause of premature tree loss in residential landscaping.

Mulch types: which for what

Hardwood bark (shredded): the workhorse. Breaks down in 1–2 years, adds organic matter. Best for shrub beds and general landscaping. $30–$45 per yard delivered.

Pine bark nuggets: larger chunks, last 2–3 years, good for slopes (won't wash away as easily). $35–$50 per yard.

Cedar: aromatic, naturally pest-resistant, lasts 3+ years but doesn't improve soil as fast. Pricier at $45–$70 per yard.

Cypress: slow to decompose, but sourced from mature trees with sustainability concerns in the southeastern US. Consider alternatives.

Rubber mulch: doesn't decompose, good for playgrounds and paths, but doesn't feed soil. $10–$15 per bag (more than wood).

Straw / pine straw: excellent for vegetable gardens. Breaks down in 6 months. Cheap — $5–$8 per bale.

Dyed wood chips (black, red, brown): budget option, but dyes fade in 3–6 months and can contain treated wood chips. Stick to natural when possible.

Bulk vs. bag: the crossover point

A 2 cubic foot bag of bagged mulch costs $3–$6 at home improvement stores. A cubic yard of bulk mulch is 13.5 cubic feet — the equivalent of ~7 bags. Priced at $30–$45 per yard plus delivery:

• Under 2 yards total: bagged is usually easier and similar total cost
• 2–4 yards: calculate delivery fee vs. bag cost. Often bulk wins.
• 5+ yards: bulk is much cheaper. 10 yards bagged = $200–$400; bulk = $350–$550 delivered.

One cubic yard of mulch covers roughly 100 sq ft at 3 inches deep. That's a typical mid-size front bed.

Pro tips from the job site

• Pull weeds before you mulch. Mulch suppresses new weeds but won't kill established ones.
• Leave a 6-inch gap around tree trunks and shrub stems. Mulch contact causes rot.
• Wet the mulch lightly after spreading. Prevents wind displacement and helps it settle.
• Don't add fresh mulch on top of compacted old mulch. Break up old layer first so water and air still reach the soil.
• For steep slopes, use larger chunks (nuggets, not shredded) and consider a natural landscape fabric underneath.
• Color fades. Dyed mulches look great for 2–3 months, mediocre for 9. Natural mulches age more gracefully.

How often to refresh mulch

• Shredded hardwood: top up with 1–2 inches annually
• Bark nuggets: every 2–3 years
• Cedar: every 3 years
• Rubber: effectively never (but it also doesn't improve soil)
• Straw in veg gardens: every growing season

Always pull back old mulch and check underneath before adding new. If the existing layer has matted down or formed a hydrophobic crust (water beads instead of absorbing), break it up with a rake before topping up.