How many cubic yards of mulch
A bed 20 by 30 feet at 3 inches deep is 600 × 0.25 = 150 cubic feet. A cubic yard is 27 cubic feet, so that is 5.56 yards; with 10% for spill and settling, 6.11. Suppliers deliver in quarter yards, so the number to give them is 6.25 cubic yards — and at the reference price here, $322.50 including one delivery. That load weighs about 2,891 pounds, which is two trips in a half-ton pickup if you fetch it yourself.
Order the step, not the bare need. Asking for 6.11 yards gets you 6.25 anyway, and asking for 6 leaves you a wheelbarrow short at the far end of the bed. The box above lets you switch the step to a half or a whole yard if that is how your supplier sells.
What one yard covers
A cubic yard is 27 cubic feet, so it spreads over 324 square feet an inch deep — and half that at 2 inches, a third at 3:
| Depth | One yard covers |
|---|---|
| 1 in | 324 ft² |
| 2 in | 162 ft² |
| 3 in | 108 ft² |
| 4 in | 81 ft² |
A yard is 13.5 of the 2 cubic foot bags, so 14 of them, whatever depth you spread it at. Fourteen bags cost $62.72 at the reference price here. Whether the yard is cheaper depends on the trip: at $38 a yard plus $85 delivered, one yard costs $123 and the bags win easily — but the 6.25 yard load above works out at $51.60 a yard, and there the bags are a fifth dearer for the same mulch. The trip charge is the whole story, which is why the block under the list compares the two at the size you actually typed.
Those coverage figures are the arithmetic without waste. The page adds the 10% in the box above before it rounds, which is why 600 square feet at 3 inches comes to 6.25 yards rather than the 5.56 the bare division gives.
Yards to order, by bed and depth
After the 10% waste box, rounded up to the quarter yard:
| Bed | Square feet | 2 in | 3 in | 4 in |
|---|---|---|---|---|
| 10 × 10 ft | 100 ft² | 0.75 | 1.25 | 1.5 |
| 10 × 20 ft | 200 ft² | 1.5 | 2.25 | 2.75 |
| 20 × 20 ft | 400 ft² | 2.75 | 4.25 | 5.5 |
| 20 × 30 ft | 600 ft² | 4.25 | 6.25 | 8.25 |
| 20 × 50 ft | 1000 ft² | 7 | 10.25 | 13.75 |
When a yard is worth it
Below about 2 cubic yards most suppliers will not drop a load at all, and the trip charge makes it pointless even where they will: that is why this page starts comparing bags against a load from there and not before. Past 6 yards or so the load is plainly cheaper, and past 10 you are into two or three trips with a trailer rather than a pickup.
Ask two things when you ring round: what the step is — quarter, half or whole yard — and whether delivery is per trip or per yard. Per trip is usual, and it is why one big order beats two small ones.
Two to four inches
The University of Illinois Extension recommends 2 to 4 inches on a bed: thinner and weeds come through, deeper and you keep air from the roots. Three inches is the middle and where this page starts. The depth box takes anything, and says so beside itself when you leave that range.