Beds are rarely neat rectangles. Pick the shape you actually have — round, triangular or L-shaped — set the depth, and get bag counts, cubic yards and how many pickup loads that is.
Two to three inches is enough to top up a bed that already has mulch on it. Three to four inches suits a new bed, or one where weeds keep coming through — that depth blocks enough light to stop most seeds germinating.
Past four inches you start causing problems. Deep mulch holds water against the soil surface, and roots that stay wet rot. It also sheds light rain before it reaches the soil, so the bed can be soaked on top and bone dry underneath.
One rule regardless of depth: keep mulch off the trunk. Piling it against bark traps moisture and invites rot and rodents. Leave a few inches of clear ground around the base.
A cubic yard is 27 cubic feet. Divide that by the depth in feet and you get the coverage. At three inches — a quarter of a foot — that's 27 ÷ 0.25 = 108 square feet.
| Depth | Coverage per yd³ |
|---|---|
| 1 in | 324 ft² |
| 2 in | 162 ft² |
| 3 in | 108 ft² |
| 4 in | 81 ft² |
| 6 in | 54 ft² |
One cubic yard takes 14 bags of the 2 ft³ size, or 9 bags of the 3 ft³ size. At $4 a bag, a yard's worth of the small size costs $56 before you have carried any of it.
Bulk mulch is usually well under that per yard, but it comes with a delivery fee that doesn't change much whether you order one yard or five. That fee is what sets the crossover point. Put your own bulk price and delivery charge against the bag total above — for most yards the answer flips somewhere around 2 to 3 cubic yards.
The other factor is handling. Bags come sealed and stack in a car boot. Bulk arrives as a pile on the driveway that has to move by wheelbarrow before it rains.
Round beds use the diameter across the widest point — the calculator squares the radius and multiplies by π for you. A triangular bed needs the base and the height measured square across from it, not the length of a sloping side.
For anything more complicated, split it into rectangles that don't overlap and add them up. The L-shape option does exactly that with two. A curved border is close enough to a rectangle of average width for a material order.
| Assumption | Value used |
|---|---|
| Small bag volume | 2 ft³ |
| Large bag volume | 3 ft³ |
| Cubic feet per cubic yard | 27 |
| Bulk order increment | 0.5 yd³ |
| Usable pickup truck load | 2 yd³ |
| Default waste factor | 5% |
Bag sizes vary by brand and by mulch type — check the bag before ordering. The pickup figure is a sensible load for a full-size bed, not a maximum; wet mulch is much heavier than dry, so check your vehicle's payload rating rather than filling to the rails.