How it works
The area of the bed times the depth is the volume. A round ring around a tree is a circle minus the small circle you leave clear at the trunk. Convert depth from inches to feet, then divide cubic feet by 27 for cubic yards.
Penn State Extension advises a 2 to 4 in layer of organic mulch, pulled 3 to 5 in back from young trees and 8 to 10 in back from mature trees so it does not press against the bark. That is why the clear circle is an input.
Worked example
An 8 ft diameter mulch ring around a tree, 3 in deep, with a 12 in circle kept clear at the trunk:
- Area = π ÷ 4 × 8² − clear circle (π ÷ 4 × (12 in ÷ 12)²) = 49.5 ft²
- Volume = 49.5 ft² × 3 in ÷ 12 = 12.37 ft³
- Cubic yards = 12.37 ÷ 27 = 0.46 yd³
- Bags = 12.37 ÷ 2 ft³, rounded up = 7
| Input | Value |
|---|---|
| Bed shape | Round ring around a tree (diameter) |
| Length, or diameter of a round bed | 8 ft |
| Width (rectangle only) | 4 ft |
| Clear circle left around the trunk | 12 in |
| Mulch depth | 3 in |
| Bag size | 2 ft³ |
| Result | Value |
|---|---|
| Mulch needed | 0.46 yd³ |
| Volume | 12.4 ft³ |
| Bags | 7 bags |
| Area covered | 49 ft² |
Assumptions and limits
- The bed is flat and mulch is loose; settling over time means you may need to top up.
- Wood chips and bark differ in bulk; the volume is the same, but weight and coverage per bag vary by product.
- Rectangle or circle only. Split an irregular bed into pieces and add them.
Common questions
How much does one cubic yard of mulch cover?
About 162 sq ft at 2 in deep, 108 sq ft at 3 in, and 81 sq ft at 4 in.
How deep should mulch be around a tree?
Penn State Extension recommends a 2 to 4 inch layer of organic mulch, pulled 3 to 5 inches away from young trees and 8 to 10 inches away from mature trees.
What is a mulch volcano?
Mulch piled against the trunk holds moisture on the bark and can lead to decay and pest problems. Keep the trunk flare clear.
How many bags are in a cubic yard?
13.5 bags of 2 cubic-foot mulch, since a cubic yard is 27 cubic feet.
Sources
- Volume of a flat layer; 1 cubic yard = 27 cubic feet.
- Penn State Extension, Mulching Landscape Trees: a 2- to 4-inch layer of organic mulch, pulled 3 to 5 inches back from young trees and 8 to 10 inches back from mature trees.
- Read them: Penn State Extension: Mulching Landscape Trees
Updated 2026-09-30