Mulch calculator
A 20 × 10 ft bed mulched 3 in deep takes 1.85 cubic yards of mulch: 25 bags of 2 cu ft or 17 bags of 3 cu ft.
How deep to mulch
Penn State Extension recommends a 2 to 4 in layer of organic mulch and no more, less on poorly drained soil, and 1 to 2 in of finely shredded or double-shredded mulch. Oregon State University Extension puts wood chips at 3 to 4 in, no deeper than 4 in, and bark at no more than 3 in. Keep mulch pulled back from tree trunks and plant stems.
If the bed already has mulch on it, measure what is left and order only the difference. Topping up a bed that has 1 in left to a 3 in layer means ordering for 2 in.
Worked example
Area: 20 ft × 10 ft = 200 sq ft
200 sq ft × 3 in = 50 cu ft ÷ 27 = 1.85 cu yd
50 cu ft ÷ 2 cu ft per bag = 25 bags
A ring of mulch 6 ft across around a tree, 3 in deep, takes 0.26 cubic yards, or 4 bags of 2 cu ft.
How far mulch goes
| Depth | Sq ft per cu yd | Sq ft per 2 cu ft bag | Sq ft per 3 cu ft bag |
|---|---|---|---|
| 1 in | 324 | 24 | 36 |
| 2 in | 162 | 12 | 18 |
| 3 in | 108 | 8 | 12 |
| 4 in | 81 | 6 | 9 |
| Bed area | Cu yd at 3 in | 2 cu ft bags | 3 cu ft bags |
|---|---|---|---|
| 50 sq ft | 0.46 | 7 | 5 |
| 100 sq ft | 0.93 | 13 | 9 |
| 200 sq ft | 1.85 | 25 | 17 |
| 300 sq ft | 2.78 | 38 | 25 |
| 500 sq ft | 4.63 | 63 | 42 |
| 1,000 sq ft | 9.26 | 125 | 84 |
A cubic yard is 27 cubic feet, so it equals 13½ bags of 2 cu ft or 9 bags of 3 cu ft. Bulk mulch is sold by the yard; the EPA lists shredded wood chips at about 500 lb per cubic yard, so a yard of dry mulch is a manageable load, though wet mulch weighs more.
Sources
- Mulching Landscape Trees, Penn State Extension, updated April 2018. A 2 to 4 in layer of organic mulch and no more; less on poorly drained soil.
- Mulching Woody Ornamentals with Organic Materials (EC 1629), Oregon State University Extension, March 2009, reviewed 2024. Wood chips 3 to 4 in deep and no more than 4 in; bark no more than 3 in; screened materials about 3 in.
- How Much Compost, Soil or Mulch Do I Need to Purchase?, Texas AgriLife Extension Service, Travis County, February 2010. Square feet times depth in inches, divided by 324, gives cubic yards.
- Standard Volume-to-Weight Conversion Factors, U.S. Environmental Protection Agency, March 2016. Loose weights of gravel, rock, sand, sandy loam soil and shredded wood chips.