Tree Mulch Ring Calculator
Calculate mulch for rings around trees, subtracting the trunk.
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What this tool does
This calculator finds the mulch needed for donut-shaped rings around trees: the ring area minus the trunk, times depth, times the number of trees — in cubic yards and 2 cu ft bags.
How to use the Tree Mulch Ring Calculator
- Enter the outer diameter of the mulch ring.
- Enter the trunk diameter.
- Enter mulch depth (2–4 in).
- Enter how many trees.
- Keep mulch 3–6 inches away from the trunk when spreading.
Formula
Area = π × (R² − r²); cu ft = Area × (D ÷ 12) × trees
- R
- Ring radius (ft)
- r
- Trunk radius (ft)
- D
- Depth (in)
Worked example
Five trees with 6 ft rings, 8 in trunks, 3 in deep.
Inputs
- Ring diameter6 ft
- Trunk diameter8 in
- Mulch depth3 in
- Number of trees5
Result
- Mulch needed1.29 cu yd
- Bags (2 cu ft)18
- Area per ring27.93 sq ft
- Total volume34.91 cu ft
Results explained
- Mulch needed
- Cubic yards for all rings.
- Bags
- 2 cu ft bags.
- Area per ring
- Mulched area around one tree.
- Total volume
- Cubic feet overall.
Frequently asked questions
At least 3–4 ft diameter for young trees; ideally out to the drip line.
2–4 inches, tapering to nothing near the trunk.
Mulch piled against the trunk — it traps moisture and invites rot and pests. Avoid it.
A 6 ft ring at 3 in needs about 7 cu ft — roughly 4 bags of 2 cu ft.
Shredded hardwood or wood chips; they break down slowly and feed soil life.