Mulch is sold in cubic yards for bulk and cubic feet for bags, while your beds are measured in square feet. This calculator handles the conversion in both directions and tells you whether bulk or bagged is the cheaper route for your project size.
Need gravel or stone instead of organic mulch? Use the Gravel Calculator for weight-based stone ordering.
Mulch Quantity Calculator
Choose your bed shape, enter dimensions and depth, and get cubic yards, bag counts, and a bulk vs bagged cost comparison.
The Mulch Volume Formula
Mulch quantity is a straightforward volume calculation. The only conversion that trips people up is inches of depth into feet, and cubic feet into cubic yards.
Cubic Yards = (Area sq ft × Depth in ÷ 12) ÷ 27
Bags = (Area sq ft × Depth in ÷ 12) ÷ Bag Size cu ft
Worked example: A 20 × 5 ft foundation bed at 3 inches deep. 20 × 5 = 100 sq ft. 3 ÷ 12 = 0.25 ft. 100 × 0.25 = 25 cubic feet. 25 ÷ 27 = 0.93 cubic yards. In 2 cubic foot bags: 25 ÷ 2 = 13 bags. At $45/yd bulk that is $42; at $4.50/bag it is $59 — bulk saves about 30% even on this small bed.
A useful shortcut: 324 divided by your depth in inches gives the square feet one cubic yard covers. At 3 inches, 324 ÷ 3 = 108 sq ft per yard. At 2 inches, 162 sq ft per yard.
Mulch Coverage by Depth
Use this table to check a quote or work backward from a delivery you have already ordered.
| Depth | Sq Ft per Cu Yd | Sq Ft per 2 Cu Ft Bag | Cu Yd per 100 Sq Ft | Bags per 100 Sq Ft |
|---|---|---|---|---|
| 1 in | 324 | 24 | 0.31 | 5 |
| 2 in | 162 | 12 | 0.62 | 9 |
| 3 in | 108 | 8 | 0.93 | 13 |
| 4 in | 81 | 6 | 1.23 | 17 |
| 6 in | 54 | 4 | 1.85 | 25 |
Six inches is included for reference only — it is too deep for planted beds and should only be used for pathways or unplanted weed-suppression areas.
Mulch Needed by Common Bed Size
Quantities shown at the standard 3-inch depth, with 2 cubic foot bag equivalents.
| Bed Size | Sq Ft | Cu Yd (3 in) | Bags (3 in) | Bulk Cost | Cheaper Option |
|---|---|---|---|---|---|
| 4 × 10 ft | 40 | 0.37 | 5 | $17 | Bags (below minimum) |
| 5 × 20 ft | 100 | 0.93 | 13 | $42 | Either — close call |
| 10 × 20 ft | 200 | 1.85 | 25 | $83 | Bulk |
| 12 ft circle | 113 | 1.05 | 15 | $47 | Either |
| 20 × 25 ft | 500 | 4.63 | 63 | $208 | Bulk (saves ~$100) |
| 30 × 40 ft | 1,200 | 11.11 | 150 | $500 | Bulk (saves ~$300) |
Bulk cost assumes $45 per cubic yard delivered. Bag cost comparison assumes $4.50 per 2 cubic foot bag. Most bulk suppliers have a 2–3 cubic yard delivery minimum.
Mulch Types, Longevity and Cost
| Type | Price/Cu Yd | Lasts | Best For | Drawback |
|---|---|---|---|---|
| Shredded Hardwood | $25–$45 | 1–2 yr | General beds, slopes | Can mat and shed water |
| Dyed Hardwood (black/brown) | $30–$55 | 1–2 yr | Curb appeal, uniform look | Color fades in 4–6 months |
| Pine Bark Nuggets | $35–$60 | 2–3 yr | Flat beds, acid lovers | Floats away on slopes |
| Pine Straw | $3–$8/bale | 6–12 mo | Slopes, azaleas, natural look | Needs frequent refresh |
| Cedar / Cypress | $45–$90 | 2–3 yr | Insect resistance, aroma | Highest cost |
| Wood Chips (arborist) | $0–$20 | 1–2 yr | Paths, large areas, budget | Inconsistent, may have weeds |
| Rubber Mulch | $90–$180 | 10+ yr | Playgrounds, permanent beds | No soil benefit, heat |
Arborist wood chips are often free from local tree services looking to avoid dump fees. They are coarser and less uniform than retail mulch but work well on paths and in informal beds.
Measuring Irregular and Curved Beds
Most real garden beds are not rectangles. Three practical approaches, in order of accuracy:
Break It Into Shapes
Divide the bed into rectangles, triangles, and half-circles, calculate each separately, and add the areas. A rectangle is length × width. A triangle is base × height ÷ 2. A circle is 3.14 × radius². This is the most accurate method for beds with distinct sections, and it takes only a few minutes with a tape measure and a sketch.
Average Width Method
For a long curving border bed, measure the length along the center of the curve, then measure the width at five or six points and average them. Multiply average width by length. On a typical foundation border this lands within 10% of the true area, which is well inside the margin you would cover with a waste allowance anyway.
Rope and Grid Method
Lay a garden hose or rope along the bed outline, then measure the smallest rectangle that fully contains the shape. Multiply length × width, then take 70–80% of that figure for a typical curved bed. This is the fastest method and is accurate enough when you plan to round your order up to the nearest half yard regardless.
Mulch Volcanoes Around Tree Trunks
Piling mulch against a trunk traps moisture against the bark, invites rot and fungal disease, and gives voles a protected place to chew the cambium layer. It is one of the most common causes of premature death in landscape trees. Mulch should form a flat donut, not a cone, with 3–6 inches of bare soil visible around the trunk flare.
Adding Fresh Mulch Without Removing Old Layers
Topping off every year without checking total depth builds up an impermeable mat that sheds water rather than absorbing it. Once accumulated depth exceeds 4 inches, roots begin growing up into the mulch layer where they dry out and die back. Measure existing depth before ordering, and rake or remove material if you are already at 3 inches.
Buying Bags for a Large Project
Bagged mulch works out to roughly $85–$140 per cubic yard equivalent, against $35–$70 for bulk delivered. On a 500 sq ft project at 3 inches deep, that difference is around $100–$200 plus the labor of hauling and opening 63 bags. Bulk becomes the clear choice above about 2 cubic yards, which is only 216 sq ft at 3 inches.
Using Landscape Fabric Under Organic Mulch
Fabric under organic mulch causes problems within two or three years. The mulch decomposes into soil on top of the fabric, weeds root in that new layer, and their roots grow through the fabric where they become nearly impossible to pull. Fabric belongs under gravel and stone, which do not decompose. Under organic mulch, a 3-inch layer alone suppresses weeds effectively.
About these price ranges
Pricing varies widely by region, season, project size, and site conditions. Treat every figure on this page as a planning estimate for budgeting only — not as a quote. Coastal metro markets commonly run 20–40% above national ranges while rural inland markets can fall 10–20% below. Always collect at least three written quotes from local contractors before committing to a budget.
Sourced figures: Clemson Cooperative Extension, HGIC 1604 (coverage formula and application depths).
Unsourced estimates: All mulch prices, bag costs, and product lifespans. These are informed planning figures rather than data drawn from a published price index, and they carry a correspondingly wider margin of error.