Use zero for the inner diameter when the entire circle is mulched. Around a tree, measure a clear unmulched center rather than placing mulch against the trunk.
01 / Formula
How this is calculated
Bed area = π × (outer radius² − inner radius²); volume = area × depth02 / Assumptions
What the estimate assumes
- ✓Both boundaries are circular and share a center.
- ✓Depth is uniform.
- ✓Bag volume comes from the product label.
03 / Worked example
See the math in context
A 16-ft bed with a 3-ft clear center contains about 194 sq ft before multiplying by mulch depth.
04 / Guidance
Protect trunks and stems
Keep mulch clear of the trunk and root flare according to appropriate horticultural guidance. The inner-diameter field makes that exclusion visible.
Questions
Frequently asked
How do I measure an irregular area?+
Split the bed or lawn into rectangles, circles, and triangles, calculate each area, then add them. Measure narrow curves in shorter sections for a better approximation.
Should I include extra material?+
Use a visible allowance for grade variation, settlement, compaction, spillage, cuts, or future repair as appropriate. The right percentage depends on the material and site.