How to use this calculator
- Measure each bed. Length and width in feet. Beds are rarely tidy rectangles, so add a section for each part — a bed that wraps around a corner of the house is two rectangles, not one guess.
- Set the depth. Three inches is the default and the right answer for most beds. The preset buttons explain when to use two or four.
- Choose your bag size. Two cubic feet is the shelf standard in the US; some brands and most soil products come in three.
If you are deciding between bagged and bulk, open the comparison panel and enter the two prices. It will tell you where the crossover falls for your supplier instead of making you do it in the parking lot.
Curved beds are easier than they look: measure the longest and shortest width, average them, and use that. The error is far smaller than the difference between a two-inch and a three-inch layer.
The formula
volume (cubic feet) = area (sq ft) × depth (in) ÷ 12
cubic yards = cubic feet ÷ 27
bags = cubic feet ÷ bag size (cu ft), rounded upWorked example — a 20 ft × 10 ft bed at 3 inches deep:
- Area: 20 × 10 = 200 sq ft
- Depth in feet: 3 ÷ 12 = 0.25 ft
- Volume: 200 × 0.25 = 50 cubic feet
- In cubic yards: 50 ÷ 27 = 1.85 cubic yards
- In 2 cu ft bags: 50 ÷ 2 = 25 bags
Twenty-five bags is about the point where hauling becomes the real cost. They fill a mid-size SUV completely, and you will be lifting roughly 1,000 lb of mulch twice — once into the car and once out of it.
Coverage per cubic yard
The shortcut worth memorising: one cubic yard covers 324 square feet one inch deep. Divide by your depth to get the coverage.
| Depth | Coverage per cubic yard | Coverage per 2 cu ft bag |
|---|---|---|
| 1 in | 324 sq ft | 24 sq ft |
| 2 in | 162 sq ft | 12 sq ft |
| 3 in | 108 sq ft | 8 sq ft |
| 4 in | 81 sq ft | 6 sq ft |
A cubic yard is 27 cubic feet, so at the standard 2 cu ft bag size you need 13.5 bags to equal one bulk yard. That number is the whole basis of the bulk-versus-bags decision.
How deep should mulch go?
| Depth | When to use it |
|---|---|
| 2 in | Around annuals, bulbs and shallow-rooted perennials |
| 3 in | General beds and around shrubs — the usual target |
| 4 in | Paths, slopes, and heavy weed pressure — the maximum |
Penn State Extension and University of Maryland Extension both put landscape mulch at two to three inches, and no more than four.
Three inches is the number to aim for because it is the point where mulch actually starts doing its job: it blocks enough light to stop most weed seeds germinating, and it holds soil moisture through a dry week. Two inches looks the same on day one and is noticeably weedier by midsummer.
Going deeper is not better. Excess mulch keeps oxygen out of the soil and suffocates the roots underneath, and it holds moisture against bark, which invites decay and gives insects and disease a way in. Keep it pulled back three to four inches from trunks and stems — the “mulch volcano” heaped against a tree is one of the most common ways to slowly kill it, and extension services are unanimous that it should never be done.
If you are topping up an existing bed, measure what is already there and add the difference. Beds that get a fresh three inches every spring are four years from being a problem.
Bulk or bagged?
Bagged mulch costs more per cubic foot, essentially always. What you are buying with the difference is convenience: bags stack in a garage, stay dry, and let you do one bed at a time.
Bulk is cheaper by volume but comes with a delivery fee and usually a minimum order. The arithmetic that matters is:
bagged total = bags × price per bag
bulk total = yards (rounded up) × price per yard + deliveryFor most suppliers the crossover lands somewhere between two and three cubic yards — around 27 to 40 bags. Below that, bags usually win once delivery is priced in. Above it, bulk pulls ahead quickly.
Two practical constraints the arithmetic does not capture. First, bulk arrives as a pile on your driveway and stays there until you move it, so you need a free weekend and somewhere it can sit. Second, a cubic yard of bark mulch weighs roughly 400 to 800 lb depending on how wet it is — one yard fills a half-ton pickup bed to about level, and two yards heaped is at the limit of what most half-ton trucks should carry.
What about the different mulch types?
Volume is volume: shredded hardwood, bark nuggets, pine straw and dyed mulch all cover the same area at the same depth. What changes is longevity and weight.
- Shredded hardwood knits together and stays put on slopes. Breaks down in a season or two.
- Bark nuggets last longer but float and wash out of anywhere water runs.
- Dyed mulch holds colour for a year or so; the dye is the point, not the wood underneath.
- Pine straw is much lighter per cubic foot and is usually sold by the bale rather than by volume, so this calculator will not help there.
This is an estimate. Bulk yards are measured loose and settle in transit; bagged mulch is compressed and fluffs up when you open it. Buy to the number here, and expect to be within a bag or two either way.