How the calculation works
Mulch, soil and stone are sold by volume, so the calculation is area times depth. The trap is units: beds are measured in feet, depth in inches and the product in cubic yards. The calculator does the conversion, but it helps to see it once:
Cubic yards = length (ft) x width (ft) x depth (in) / 324
The 324 comes from 12 inches in a foot times 27 cubic feet in a cubic yard. A bed 20 feet long and 5 feet wide at 3 inches deep is 20 x 5 x 3 / 324 = 0.93 cubic yards. For a circle, the area is 3.14 x radius squared; a 10 foot round bed is 78.5 square feet.
How deep to spread
| Use | Depth | Notes |
|---|---|---|
| Mulch in established beds | 2 to 3 in | Top up 1 in each spring instead of redoing it |
| Mulch for weed control on open ground | 3 to 4 in | Lay cardboard first and it works far better |
| Mulch around shallow-rooted plants and annuals | 1 to 2 in | Deeper smothers roots |
| Topsoil to level a lawn | 0.5 to 1 in per pass | Grass dies under more than an inch at once |
| Topsoil for a new lawn or bed | 4 to 6 in | Mix into the existing soil rather than layering |
| Raised bed soil | Full box depth | Settles about 10 percent after watering; fill a little high |
| Gravel path or driveway base | 3 to 4 in | Compacted crushed stone, then 1 to 2 in of finish gravel |
| Pea gravel or river rock as ground cover | 2 to 3 in | Over landscape fabric to stop it sinking |
Keep mulch 3 to 4 inches away from tree trunks and off the wood of the house. Piled against bark it holds moisture and invites rot and insects; piled against siding it bridges the termite barrier.
Bags or bulk
A cubic yard is 27 cubic feet: 13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet. Bags are easy to carry, keep the product dry and suit anything under half a yard. Above about 10 bags, bulk delivered by the yard is almost always cheaper, even with a delivery fee, and you avoid the plastic. Most suppliers deliver from one yard and charge a flat fee within a radius, so it pays to order everything for the season in one drop.
If you collect bulk material yourself, mind the weight. The calculator shows an approximate weight and pickup loads based on a half-ton truck's usable payload of around 1,500 pounds. Two yards of dry mulch is a normal load; two yards of wet topsoil is more than double the truck's limit.
How much a cubic yard weighs
| Material | Weight per cubic yard | Fits in a half-ton pickup |
|---|---|---|
| Bark or hardwood mulch, dry | 400 to 800 lb | About 2 yards |
| Compost | 800 to 1,200 lb | About 1.5 yards |
| Garden soil mix | 1,500 to 2,000 lb | Under 1 yard |
| Topsoil | 2,000 to 2,400 lb | About two-thirds of a yard |
| Sand or pea gravel | 2,500 to 2,700 lb | About half a yard |
| Crushed stone or gravel | 2,600 to 2,900 lb | About half a yard |
Wet material weighs noticeably more; topsoil after rain can be 30 percent heavier than the dry figure.
Coverage of one cubic yard
| Depth | One cubic yard covers | One 2 cu ft bag covers |
|---|---|---|
| 1 inch | 324 sq ft | 24 sq ft |
| 2 inches | 162 sq ft | 12 sq ft |
| 3 inches | 108 sq ft | 8 sq ft |
| 4 inches | 81 sq ft | 6 sq ft |
| 6 inches | 54 sq ft | 4 sq ft |
Measuring odd-shaped beds
Break the bed into rectangles and circles and add each as a separate area in the calculator. For a kidney-shaped bed, measure the longest length and the average width and treat it as a rectangle; the error is small. For a border that runs along a fence, pace the length and measure the width in three places. Round up at the end rather than on each piece: a bag or two spare is useful for topping up around plants, and a bulk yard short means a second delivery fee.
Having it delivered and spread
A landscaper with a dump trailer will deliver, spread and edge the beds in a morning, and many include the material at trade price. For a whole-yard refresh of 5 yards or more it is often not much dearer than doing it yourself. Landscapers on ProBusiness101 list their services and show photos of finished beds, so you can see the standard of work before asking for a quote.