Buying mulch comes down to three numbers: the area of your beds, the depth you want, and the unit you are buying in. This guide explains how to get each one right, from measuring curved beds to mulching around trees. The mulch calculator does the arithmetic.
The short answer
Cubic yards = area (ft²) × depth (in) ÷ 324
At the usual 3 inch depth, one cubic yard covers 108 ft². A 2 cu ft bag covers 8 ft² and a 1.5 cu ft bag covers 6 ft², which matches the coverage table on Scotts' mulch FAQ.
Step 1: Measure your beds
Rectangular beds
Measure length and width in feet and multiply. A 24 × 4 ft bed along a fence is 96 ft².
Curved and kidney-shaped beds
Measure the length, then take the width at three or four evenly spaced points and average them. Multiply the length by the average width.
Example: a 16 ft curved bed with widths of 3, 5, 6 and 4 ft has an average width of 4.5 ft. 16 × 4.5 = 72 ft².
Round beds and tree rings
Area = π × radius². A ring 8 ft across has a radius of 4 ft: 3.1416 × 16 = 50.27 ft².
Beds around a central feature
If a bed surrounds something you won't mulch, such as a birdbath base, a utility box or a tree trunk zone, subtract that area.
Example: a 10 ft round bed with a 2 ft round birdbath base. π × 5² − π × 1² = 78.54 − 3.14 = 75.4 ft².
Many beds
Measure each bed and add the areas. A simple list, with one line per bed and the total at the bottom, avoids missed beds. Then use one depth for the total, or run beds with different depths separately.
Step 2: Choose the depth
| Mulch type or situation | Depth | Source |
|---|---|---|
| Weed barrier in general beds | 2–3 in | Scotts |
| Fine textured or composted mulch | 2–3 in | University of Illinois Extension |
| Coarse mulch such as wood chips | 3–4 in | University of Illinois Extension |
| Around trees | no more than 2–4 in | University of Vermont Extension |
More is not better. Illinois Extension notes that thick layers can mat, cutting off water and oxygen to the soil, and can give rodents a place to hide. UVM Extension says that more than 4 inches can encourage adventitious roots, which grow from the trunk and can eventually girdle a tree.
Topping up
Measure the depth of the old mulch first by pushing a ruler down to the soil in a few spots. If 1 inch remains and you want 3, buy for 2 inches. Scotts says old mulch generally doesn't need to be removed unless the layer is more than 4 inches thick. Loosen matted mulch before topping up.
Step 3: Convert to what you are buying
Cubic feet and yards
- Cubic feet = area × depth (in) ÷ 12.
- Cubic yards = cubic feet ÷ 27.
Example: the beds above total 96 + 72 + 50.27 = 218.27 ft². At 3 in: 218.27 × 3 ÷ 12 = 54.57 ft³ = 2.02 yd³.
Bags
Divide cubic feet by the bag size and round up:
| Bag | Bags for 54.57 ft³ | Bags per yd³ |
|---|---|---|
| 1.5 cu ft | 37 | 18 |
| 2 cu ft | 28 | 13.5 |
| 3 cu ft | 19 | 9 |
Quick reference: cubic yards needed by area
| Area | 2 in | 3 in | 4 in |
|---|---|---|---|
| 50 ft² | 0.31 yd³ | 0.46 yd³ | 0.62 yd³ |
| 100 ft² | 0.62 yd³ | 0.93 yd³ | 1.23 yd³ |
| 200 ft² | 1.23 yd³ | 1.85 yd³ | 2.47 yd³ |
| 500 ft² | 3.09 yd³ | 4.63 yd³ | 6.17 yd³ |
| 1,000 ft² | 6.17 yd³ | 9.26 yd³ | 12.35 yd³ |
Step 4: Decide between bags and bulk
To compare, convert both to a price per cubic yard:
- Bags: bag price × bags per yard (13.5 for 2 cu ft bags, 18 for 1.5 cu ft).
- Bulk: price per yard + (delivery fee ÷ yards ordered).
Bulk usually wins on larger jobs, but it comes as a pile on the driveway that you move by wheelbarrow. Bags cost more per yard but are easy to carry, store and spread in small beds. We don't quote prices because they vary widely by region and product. Get local quotes using your cubic yard figure.
Mulching around trees
Tree rings are where mulch does the most good and the most harm.
- Shape: a wide, flat ring like a donut, not a cone. University of Vermont Extension calls piled-up cones "mulch volcanoes". They hold moisture against the bark, which encourages decay, insects and disease, and they bury the root flare.
- Gap at the trunk: Illinois Extension says to keep mulch at least 4 inches from the trunk. UVM describes the "3-3-3" rule many arborists use: at least 3 inches from the trunk, no more than 3 inches deep, and 3 feet in diameter.
- Width: extend the ring toward the drip line, the edge of the canopy, where practical.
Example: a 3-3-3 ring on a mature tree is 3 ft across at 3 in deep: π × 1.5² × 3 ÷ 12 = 1.77 ft³. One 2 cu ft bag covers it, with the trunk gap left bare.
Choosing a mulch
Scotts notes that wood and other organic mulches improve the soil as they break down. It also notes that dark mulches absorb heat, so lighter colours may suit very warm climates. Inorganic mulches such as stone don't break down and don't need yearly topping up. Because stone is much heavier, use the gravel calculator and check the weight per yard with your supplier.
When to mulch
Scotts suggests refreshing mulch about once a year. Mulch insulates the soil, conserves moisture by slowing evaporation, and suppresses weeds by blocking light. Before mulching:
- Weed the bed thoroughly. Mulch suppresses new weed seeds but won't kill established weeds.
- Edge the bed so the mulch has a clean border.
- Water the soil if it is dry.
- Spread the mulch evenly with a rake, keeping it back from stems and trunks.
Common mistakes
- Depth in feet instead of inches. 3 ft is 12 times 3 in.
- Re-applying the full depth every year. Measure what is left first.
- Volcano mulching around trees. Keep it flat and away from the trunk.
- Ignoring bag size. A "bag" can be 1.5, 2 or 3 cu ft. Read the label.
- No spare. Fresh mulch spreads unevenly. One extra bag is cheap insurance.
Frequently asked questions
How many square feet does a yard of mulch cover?
108 ft² at 3 in, 162 ft² at 2 in, and 81 ft² at 4 in.
How many bags of mulch do I need for a 10 × 10 bed?
At 3 in: 25 ft³, which is 13 × 2 cu ft bags or 17 × 1.5 cu ft bags.
Is 2 inches of mulch enough?
For fine or composted mulch and for perennial beds, yes. Illinois Extension recommends 2–3 inches for fine material. Coarse wood chips are usually applied at 3–4 inches.
How far should mulch be from a tree?
At least 4 inches, according to University of Illinois Extension. UVM Extension cites at least 3 inches under the 3-3-3 rule.
How often should I add mulch?
About once a year, as Scotts recommends. Check the depth first and top up only the difference.
Sources
- Scotts Miracle-Gro, Mulch & Soil FAQs: coverage of 1.5 cu ft bags at 3 in, a 2–3 in layer for weeds, removal over 4 in, annual mulching, dark mulch absorbs heat. https://scottsmiraclegro.com/en-us/support/help-center/mulchessoils.html
- University of Illinois Extension, "Proper Mulching Techniques": 2–4 in, fine 2–3 in, coarse 3–4 in, at least 4 in from the trunk, matting. https://extension.illinois.edu/sites/default/files/proper%5Fmulching%5Ftechniques%5Finfosheet.pdf
- University of Vermont Extension, "Beware the Mulch Volcano": volcano mulching, adventitious roots over 4 in, the 3-3-3 rule. https://www.uvm.edu/extension/news/beware-mulch-volcano
- NIST Handbook 44 (2026), Appendix C: 1 yd³ = 27 ft³. https://www.nist.gov/document/2026-nist-handbook-44-appendix-c