How the calculator works it out
Each bed is an area times a depth. The calculator adds the beds, converts cubic feet to cubic yards (the unit landscape yards sell in) and divides by the bag size for a bag count. For gravel it multiplies cubic yards by a weight range to get tons. If you enter prices, it prices the job in bags and in bulk and works out where the two cross.
Rectangle: length × width × depth (in) ÷ 12 = cubic feet
Circle: 3.1416 × (diameter ÷ 2)² × depth (in) ÷ 12 = cubic feet
Cubic yards = cubic feet ÷ 27 · Bags = cubic feet ÷ bag size, rounded up
Gravel tons = cubic yards × 1.4 to 1.7
Worked example: a border and a round bed
A 20 × 4 ft border at 3 inches deep holds 20 × 4 × 3 ÷ 12 = 20 cubic feet. A round bed 6 ft across at 3 inches holds 3.1416 × 3² × 0.25 = 7.07 cubic feet. Together that is 27.07 cubic feet, or 1.00 cubic yard: 14 bags of 2 cubic foot mulch. At $4 a bag that is $56. Bulk at $35 a yard, loaded in half yards, means paying for 1.5 yards ($52.50) plus a $60 delivery fee: $112.50. Bags win. The same beds in pea gravel 3 inches deep need 55 half-cubic-foot bags, or 1.4 to 1.7 tons. These two beds are loaded when the page opens.
Bags or bulk: the break-even
A bag price turns into a price per cubic yard: bag price × 27 ÷ bag size. A $4 bag of 2 cubic feet is $54 a yard. If bulk costs $35 a yard, every yard saves $19, and the $60 delivery fee is paid back after 60 ÷ 19 = 3.2 yards. Below that, bags are cheaper; above it, bulk. Rounding matters near the line, so the calculator also prices your exact job both ways, with whole bags and bulk rounded up to the yard's loading step.
How far a cubic yard goes
| Depth | One cubic yard covers | One 2 cu ft bag covers |
|---|---|---|
| 2 in | 162 sq ft | 12 sq ft |
| 3 in | 108 sq ft | 8 sq ft |
| 4 in | 81 sq ft | 6 sq ft |
| 6 in | 54 sq ft | 4 sq ft |
What the numbers are based on
- Bag sizes. The defaults are sizes stocked at large home centers: 2 cubic foot mulch bags (Lowe's carries Sta-Green mulch in this size; many Home Depot stores sell 1.5 cubic feet), 0.5 cubic foot pea gravel and 0.75 cubic foot topsoil. Change the bag size to match what you are buying.
- Gravel weight. 1.4 to 1.7 tons per cubic yard is a typical range for dry gravel and crushed stone, not a standard. Real weight depends on the rock and the moisture, so it is an editable default. The supplier's figure is the one that matters, because trucks are loaded by weight.
- Unit conversions. A cubic yard is exactly 27 cubic feet, and a cubic foot is exactly 0.028316846592 cubic meters (from the foot defined as 0.3048 m).
Before you order
- Fresh mulch settles. If the bed already has old mulch, measure only the depth you are adding.
- Under gravel paths, a compacted base layer is a separate material; work it out as its own bed with its own depth.
- Check whether the delivery fee covers the whole order or is charged per load, and whether the truck can reach where you want the pile.
Questions people ask
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it takes 13.5 bags of 2 cubic foot mulch, 18 bags of 1.5 cubic foot mulch or 54 bags of half-cubic-foot stone. In practice you buy whole bags, so 14, 18 or 54.
How deep should mulch be?
Most guidance for garden beds is 2 to 3 inches of wood mulch, with more around trees kept back from the trunk. The calculator starts at 3 inches for mulch, 2 inches for decorative gravel and 4 inches for topsoil, and you can set a different depth for every bed.
How many tons is a cubic yard of gravel?
Typically 1.4 to 1.7 tons, depending on the rock, the size of the stones and how wet it is. Quarries and landscape yards sell gravel by the ton and know the weight of their own material, so ask for their figure and type it in. The calculator shows both ends of the range until you do.
Is it cheaper to buy mulch in bags or in bulk?
Bulk is usually cheaper per yard but carries a delivery fee, so it only wins on bigger jobs. Enter the bag price, the bulk price per yard and the delivery fee: the calculator prices your job both ways and shows the break-even size. With $4 bags of 2 cubic feet ($54 a yard), and bulk at $35 a yard plus $60 delivery, bulk wins above about 3.2 cubic yards.
How do I measure a round or curved bed?
For a round bed, measure straight across the middle for the diameter and choose "Circle". For a kidney-shaped or curved bed, measure the longest length and the average width and use a rectangle; it will be close, and the bags round up anyway.
How much does a bag of topsoil cover?
A 0.75 cubic foot bag spread 2 inches deep covers 0.75 × 12 ÷ 2 = 4.5 square feet, and at 4 inches about 2.25 square feet. That is why filling a raised bed from bags adds up quickly: a 4 × 8 ft bed 12 inches deep holds 32 cubic feet, or 43 bags.