Guide
How Much Mulch Do I Need?
Measure your bed, multiply by depth, divide by 324, and you have the cubic yards of mulch you need. Formula, worked examples, and a coverage table.
The short answer
To find how much mulch you need, measure the bed in square feet, then use: square feet × depth (inches) ÷ 324 = cubic yards. A 200 sq ft bed at 3 inches deep needs about 1.85 cubic yards — roughly 25 bags of 2 cu ft mulch. Use 3″ for new beds, 2″ to top up old ones.
Try it — Mulch Calculator
Full calculatorEnter a bulk price to estimate cost.
You need
0.93cu yd
- Cubic feet
- 25 cu ft
- Cubic yards
- 0.93 cu yd
- Bags (2 cu ft)
- 13 bags
- Weight
- ≈ 0.42 tons
Bulk is sold by the yard — order 1 cu yd to have enough.
The mulch formula (and the ÷324 shortcut)
Mulch is sold by volume, but you measure beds by area. One shortcut bridges the gap:
Cubic yards = square feet × depth (in inches) ÷ 324.
The 324 just folds two conversions into one. Inches to feet is ÷12. Cubic feet to cubic yards is ÷27. Multiply those (12 × 27) and you get 324.
Want the long way? It's three steps:
- Area (sq ft) = length × width. For a circle, use π × radius².
- Volume (cu ft) = area × depth in inches ÷ 12.
- Cubic yards = cubic feet ÷ 27.
Worked examples
Here is the formula on two common bed shapes.
A rectangular bed, 20 ft × 10 ft, 3″ deep:
- Area = 200 sq ft.
- 200 × 3 ÷ 324 = 1.85 cubic yards.
- That's 50 cu ft of mulch, or 25 bags at 2 cu ft each.
A round bed, 10 ft across, 3″ deep:
- Area = π × 5² ≈ 78.5 sq ft.
- 78.5 × 3 ÷ 324 ≈ 0.73 cubic yards.
- That's about 19.6 cu ft, or 10 bags.
Pro tip
Bulk mulch (by the cubic yard, delivered) is usually cheaper once you need more than about 1 cubic yard — roughly 13–14 bags. Below that, bagged is simpler. Filling a bed instead? The raised-bed soil guide runs the same math for soil.
How far one cubic yard goes
Depth changes coverage a lot. One yard of mulch covers nearly half as much ground at 4″ as it does at 2″.
| Depth | Coverage per cubic yard |
|---|---|
| 2″ | 162 sq ft |
| 3″ | 108 sq ft |
| 4″ | 81 sq ft |
Buying by the bag instead? Here's how bags add up to a yard.
| Bag size | Bags per cubic yard |
|---|---|
| 2 cu ft | 13.5 |
| 3 cu ft | 9 |
How deep should mulch be?
For most beds, 2 to 3 inches is plenty. Iowa State University Extension recommends keeping organic mulch in the 2-to-4-inch range and pulling it back from trunks and stems.
- 2 inches — a top-up over mulch that's already there.
- 3 inches — the sweet spot for new beds. It blocks weeds and holds moisture.
- 4 inches — heavier weed control in open ground. Keep it off stems and trunks.
Mulch settles and breaks down over a season, so plan to add 1 to 2 inches each year rather than starting fresh. Spreading compost first? The compost guide sizes that layer the same way.
Common mistake
Volcano mulching is piling mulch high against a tree trunk or plant stem. It traps moisture and invites rot, insects, and disease. Keep mulch a few inches clear of every trunk and stem.
Order a little extra
Beds are rarely flat, and fresh mulch settles. Add about 5 to 10 percent to your number so you don't run short near the end of the job. A leftover bag or two is easy to use up. A second trip to the store is not.
Need the numbers for your exact bed? Open the Mulch Calculator. Enter your dimensions and depth, and it returns cubic yards, bags, and cost in seconds.
Common questions
How many bags of mulch are in a cubic yard?
About 13.5 bags if each bag holds 2 cubic feet (27 ÷ 2), or 9 bags at 3 cubic feet each.
How much does a cubic yard of mulch cover?
108 sq ft at 3 inches, 162 sq ft at 2 inches, or 81 sq ft at 4 inches deep.
Does mulch settle or break down?
Yes. Organic mulches compact and decompose over a season, so plan to top up by 1–2 inches each year rather than starting over.
Bagged or bulk — which is cheaper?
Bulk (by the yard, delivered) usually wins above about 1 cubic yard. Bagged is more convenient for small jobs.
Sources
Agronomic claims in this guide are checked against these primary sources.
- Mulches for the Garden — Iowa State University Extension
Keep reading
How Much Soil for a Raised Bed?
Length times width times height in feet, divided by 27, gives cubic yards. A 4x8 bed at 10 inches needs about 1 cubic yard. Formula, bag list, and a calculator.
Read →How Much Compost Do I Need?
Multiply square feet by depth in inches, divide by 324 for cubic yards of compost. Formula, worked examples, and a bagged-vs-bulk guide.
Read →How Much Topsoil Do I Need? (Tons, Yards + Calculator)
Topsoil is sold by the ton. Multiply your square feet by depth in inches, divide by 324 for cubic yards, then plan for about 1.2 tons per yard.
Read →Mulch 101: Types, Depth, and How Much You Need
A plain-English guide to mulch — what it does, the organic and inorganic types, how deep to lay it, and how to figure out how much you need with the square feet × depth ÷ 324 formula.
Read →How Many Bags of Mulch Are in a Yard?
A cubic yard of mulch is 27 cubic feet, so it takes 14 bags of 2 cu ft mulch or 9 bags of 3 cu ft to make a yard. Tables and the ÷ math inside.
Read →