How to use the mulch calculator
- Measure each bed. For a rectangle, measure the length and width in feet. For a tree ring, measure across the circle. For a curving border, either break it into rough rectangles or pace it out and enter the square footage directly.
- Enter how many identical beds you have — useful for a row of tree rings or matching borders on both sides of a walk.
- Choose the depth. Three inches is the usual target for a new bed. If you're topping up existing mulch, enter only the amount you're adding.
- Add extra for settling if you like. Freshly spread mulch settles as it's watered. The default is 0%; for fluffy shredded bark, 5–10% extra keeps the bed at your target depth.
- Pick your bag size from the label. Bagged mulch is sold by volume, so a 2 cu ft bag holds 2 cubic feet whatever the brand.
A common mistake is measuring the whole yard instead of the planted area. Leave out patios, paths and the footprint of large shrubs you won't be mulching under.
The mulch formula
Cubic yards = cubic feet ÷ 27
Bags = cubic feet ÷ bag size (cu ft), rounded up
Depth is divided by 12 to turn inches into feet. A cubic yard is 27 cubic feet, which is why a yard of mulch equals 13.5 two-cubic-foot bags.
Worked example: a 12 × 9 ft bed at 3 inches
12 × 9 = 108 sq ft. At 3 in deep: 108 × 3 ÷ 12 = 27 cubic feet, which is exactly 1 cubic yard. In 2 cu ft bags that's 27 ÷ 2 = 13.5, so you'd buy 14 bags. With 10% extra for settling, it becomes 29.7 cubic feet (1.10 cubic yards), or 15 bags.
Worked example: three tree rings
Three rings, each 8 ft across, cover 3 × 50.3 = 150.8 sq ft. At 3 in that's 37.7 cubic feet, or 1.40 cubic yards — 26 bags of 1.5 cu ft, since 37.7 ÷ 1.5 = 25.1 rounds up.
Mulch coverage chart
How far a cubic yard or a single bag goes at common depths:
| Depth | 1 cubic yard covers | One 2 cu ft bag covers | One 3 cu ft bag covers |
|---|---|---|---|
| 1 in | 324 sq ft | 24 sq ft | 36 sq ft |
| 2 in | 162 sq ft | 12 sq ft | 18 sq ft |
| 3 in | 108 sq ft | 8 sq ft | 12 sq ft |
| 4 in | 81 sq ft | 6 sq ft | 9 sq ft |
US bags are labelled in cubic feet and metric bags in liters; the sizes are not direct equivalents, so each is listed with its true conversion:
| Bag size | Equivalent | Bags per cubic yard | Bags per m³ |
|---|---|---|---|
| 1.5 cu ft | 42.5 L | 18 | 23.5 |
| 2 cu ft | 56.6 L | 13.5 | 17.7 |
| 3 cu ft | 85 L | 9 | 11.8 |
| 40 L | 1.41 cu ft | 19.1 | 25 |
| 50 L | 1.77 cu ft | 15.3 | 20 |
| 60 L | 2.12 cu ft | 12.7 | 16.7 |
| 70 L | 2.47 cu ft | 10.9 | 14.3 |
Bag sizes vary by brand and store, so check the label before you buy. Mulch also settles a little after it's spread and watered, so a bed raked to an even 3 in will look slightly thinner after a few weeks — use the Extra for settling field (5–10% for fluffy bark) if you want to make up for it.
Bulk or bags?
Bags are clean, easy to carry and store, and the right choice for a few small beds or a quick top-up. Bulk mulch is sold by the cubic yard and is usually the better deal once you need more than a yard or two — remember that each yard replaces 13.5 two-cubic-foot bags, and all that plastic. Enter both a bag price and a bulk price above to compare, and remember to add any delivery charge to the bulk cost.
If you take delivery, have it dumped on a tarp close to the beds, and try to spread it within a week or two; a large pile left sitting for weeks can heat up and turn sour inside.
New beds vs. refreshing old mulch
- New or bare beds: 2–3 in. Coarse bark nuggets can go to 3–4 in because they settle less and let water through easily.
- Annual refresh: mulch breaks down over time, but often not all of it in one year. Dig in with a trowel and measure what's left, then add only enough to bring the total back to 2–3 in — often 1–2 in.
- Matted old mulch: rake it to break up the crust before topping up, so water can soak through.
Starting a new bed from scratch? Work out the soil first with the topsoil calculator. For a stone border or decorative rock instead of mulch, use the gravel calculator.
Frequently asked questions
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it equals 13.5 bags of 2 cu ft, 18 bags of 1.5 cu ft, or 9 bags of 3 cu ft.
How much area does a yard of mulch cover?
About 324 sq ft at 1 inch deep, 162 sq ft at 2 inches, 108 sq ft at 3 inches, and 81 sq ft at 4 inches.
How deep should mulch be?
Two to three inches is the usual recommendation for garden beds. Thinner layers let weeds through; much more than 4 inches can keep air and water from reaching roots. Keep mulch pulled back a few inches from trunks and stems.
How many bags of mulch do I need for a 10 × 10 bed?
A 10 × 10 ft bed is 100 sq ft. At 3 inches deep it needs 25 cubic feet, which is 12.5 bags — so buy 13 bags of 2 cu ft (about 0.93 cubic yards).
Should I remove old mulch before adding new?
Usually not. Measure how much is left, break up any matted crust with a rake, and add just enough to bring the total back to 2–3 inches. Remove it only if it is far too deep or piled against trunks.