How to use the mulch calculator
- Enter the bed length and width.
- Enter the depth. Extension services recommend roughly 2–4 in depending on soil (see below).
- Enter the bag size if you are buying bags; 2 cu ft is a common size.
The calculator shows bulk volume (how landscape suppliers sell mulch), the number of bags and how much area one bag covers at your depth. Once you know the volume, compare bagged and bulk prices; for larger beds, Decoratoradvice often finds bulk delivery is cheaper.
Mulch formula
Volume = length × width × depth (all in feet)
Cubic yards = volume ÷ 27
Bags = volume ÷ bag size, rounded up
Area per bag = bag size ÷ depth
Worked example
A 20 × 4 ft bed, 3 in deep, 2 cu ft bags:
20 × 4 × 0.25 = 20 cu ft
20 ÷ 27 = 0.74 cu yd
20 ÷ 2 = 10 bags
One bag covers 2 ÷ 0.25 = 8 sq ft
How deep should mulch be?
| Source | Recommendation |
|---|---|
| Iowa State University Extension | 3–4 in of wood chips or shredded bark on well-drained sites; 2–3 in on heavy soils |
| University of Florida, Florida-Friendly Landscaping | 2–3 in |
Both advise keeping mulch away from tree trunks rather than piling it against them.
Bulk or bags?
Bags are easy for small beds and refreshing a thin layer. For larger areas, bulk delivery by the cubic yard is usually simpler; one cubic yard equals 13.5 bags of 2 cu ft.
Tips
- Measure curved beds by estimating an average length and width, or use the square footage calculator for circles.
- Refresh an existing layer rather than adding a full depth on top of old mulch.
- For new beds, add soil first with the topsoil calculator, then mulch.
- Decorative stone instead of mulch is sold by weight; use the gravel calculator.
Common mistakes
- Leaving depth in inches. 20 × 4 × 3 = 240 is not cubic feet.
- Piling mulch against trunks. Both extension sources advise against it.
- Covering old mulch with a full new layer every year, which builds up too much depth.
Frequently asked questions
How much area does a cubic yard of mulch cover?
At 3 in deep, 108 sq ft; at 2 in, 162 sq ft. The cubic yard calculator has a table for other depths.
How many bags of mulch are in a yard?
13.5 bags of 2 cu ft, since a cubic yard is 27 cu ft.
How deep should mulch be?
Iowa State University Extension suggests 3–4 in on well-drained sites and 2–3 in on heavy soils; the University of Florida's program recommends 2–3 in.
How far does a 2 cu ft bag of mulch go?
8 sq ft at 3 in deep, or 12 sq ft at 2 in.
Should mulch touch the tree trunk?
No. Iowa State advises keeping it at least 6 in from trunks, and the Florida program says 12–18 in.
Can I use this for lawn soil?
Use the topsoil calculator, which allows for settling, or the sod calculator for turf.
Key takeaways
- Cubic yards = length × width × depth (in feet) ÷ 27.
- A 2 cu ft bag covers 8 sq ft at 3 in deep.
- Extension services recommend about 2–4 in, depending on soil.
- Keep mulch away from tree trunks.