How much mulch do you need?
The amount depends on two things: the area you are covering and how deep the layer should be. Mulch is sold in bags measured in cubic feet (usually 2 or 3 cubic feet) and in bulk by the cubic yard. This calculator gives you both so you can compare buying bags with having a load delivered.
How to calculate mulch by hand
- Measure the length and width of the bed in feet and multiply to get square feet.
- Pick a depth in inches and divide it by 12 to get feet.
- Multiply the area by the depth in feet to get cubic feet.
- Divide by 27 to get cubic yards.
Mulch depth guide
| Depth | Use | Coverage per cubic yard |
|---|---|---|
| 1 inch | Top-up only | 324 sq ft |
| 2 inches | Refresh an existing bed | 162 sq ft |
| 3 inches | New beds, around trees and shrubs | 108 sq ft |
| 4 inches | Heavy weed suppression | 81 sq ft |
Where does 324 come from? One cubic yard is 27 cubic feet. Spread 1 inch deep (1/12 foot), that covers 27 × 12 = 324 square feet. Divide by the depth in inches for other depths.
Bags or bulk?
- Bags are easy to carry and good for small jobs. A 2 cubic foot bag holds about one-thirteenth of a cubic yard, so 13 or 14 bags make a yard.
- Bulk mulch is usually cheaper per cubic yard once you need about 2 or more yards, but you need a place to dump it and a wheelbarrow.
- A cubic yard equals 13.5 bags of 2 cu ft, or 9 bags of 3 cu ft.
Bag sizes vary by brand, and some bags are sold by the quart rather than the cubic foot, so check the label.
Tips for spreading mulch
- Do not pile it against trunks. Leave a few inches of space so bark stays dry.
- Pull weeds first and edge the bed so the mulch stays in place.
- Do not go too deep. More than 4 inches can hold too much moisture and keep air from the roots.
- Order a little extra. Mulch settles and breaks down over the season.
Choosing a mulch material
Shredded hardwood bark, pine bark nuggets, pine straw, wood chips and compost-based mulch all work. Finer mulch packs down more and breaks down faster, so you may top it up each year. Coarse bark nuggets last longer and are often used on slopes and paths. Whatever you choose, the volume calculation is the same, because suppliers sell all of them by volume.
Fresh wood chips straight from a tree service are often free or cheap and work well for paths and around established plants. Check that they do not contain material you do not want in your garden.
Common mistakes
- Using inches as feet. A 3 inch layer is 0.25 feet.
- Forgetting curved edges. Measure the widest and narrowest points and use the average width, or split the bed into rectangles.
- Not subtracting what is already there. If old mulch is 1 inch deep and you want 3, you only need to add 2 inches.
- Buying bags by weight. Mulch bags are sold by volume. Use cubic feet to compare.
Mulch for trees, paths and borders
Around a tree, spread mulch in a wide ring rather than a tall cone, and pull it back from the trunk. For a circular tree ring, find the area with pi times the radius squared and subtract the small circle around the trunk, then enter the result as total square feet. For paths, a depth of 3 to 4 inches stops weeds better than a thin layer. For narrow borders, measure the length and the average width. A border 40 ft long and 2 ft wide is 80 sq ft, and at 3 inches deep it needs about 0.74 cubic yards, or 20 bags of 1 cubic foot.