How it works
The calculator multiplies the bed area by the mulch depth to get the volume, then divides by the bag size if you enter one.
Area = Length × Width
Volume = Area × Depth
Bags = ⌈ Volume ÷ Bag size ⌉
⌈ ⌉ means rounding up to the next whole bag. The volume itself is not rounded.
In US units this is the same as the University of California Agriculture and Natural Resources rule: square feet × depth in inches ÷ 324 = cubic yards. Units are converted internally, so a bed in feet, a depth in inches and a bag size in cubic feet or liters all work together.
Worked example
Inputs
- Measure by
- Dimensions
- Bed length
- 20 ft
- Bed width
- 4 ft
- Mulch depth
- 3 in
- Bag size
- 2 cu ft
Result
- Mulch volume
- 0.741 cu yd (20 cu ft)
- Bags
- 10
Common mistakes
- Entering depth in feet instead of inches. Three inches is a quarter of a foot; a wrong unit multiplies the order by twelve.
- Measuring the whole yard instead of the beds. Measure each bed separately and leave out paths and paved areas.
- Assuming all bags are the same size. Bag volume varies by product; read the label.
- Comparing a bag price with a bulk price per cubic yard without converting. One cubic yard is 27 cubic feet.
Assumptions and limits
- The bed is a rectangle, or you have entered its total area, and the depth is the same everywhere.
- The volume is the area times the depth, with no allowance for settling, compaction or spillage.
- Bags are rounded up to whole bags. Without a bag size, only the bulk volume is shown.
Frequently asked questions
How do I work out cubic yards of mulch by hand?
University of California Agriculture and Natural Resources gives a simple rule – square feet × depth in inches ÷ 324 = cubic yards. The 324 is 27 cubic feet per cubic yard × 12 inches per foot.
How deep should mulch be?
It depends on the type of mulch, the plants and your climate, so this calculator doesn’t suggest a figure. Check with your local extension service or the mulch supplier.
How many bags of mulch are in a cubic yard?
Divide 27 cubic feet by the bag size. For 2 cu ft bags that is 13.5, so 14 bags; for 3 cu ft bags it is 9.
Can I use this for compost, bark or pine straw?
For loose materials spread in a layer, such as compost or bark, yes. Products sold by coverage rather than volume, such as baled pine straw, need the supplier’s coverage figure instead.
Sources
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
- Mulch calculation (area × depth in inches ÷ 324 = cubic yards) — University of California Agriculture and Natural Resources. Cubic yards of mulch = square feet × depth in inches ÷ 324.
- Scotts Nature Scapes Mulch 2 cu ft; Scotts Premium Topsoil — ScottsMiracle-Gro. Example bag sizes: mulch 2 cu ft (https://scottsmiraclegro.com/en-us/8840244.html), topsoil 0.75 cu ft.
Method reviewed November 2, 2026