Mulch Calculator

How deep should mulch be?

Extension guidance converges on 2 to 4 inches. Illinois Extension recommends a 2 to 4 inch layer on well-drained sites, with composted materials at 2 to 3 inches and coarse mulches at 3 to 4³. Penn State says the same for well-drained soils, less on poorly drained ones, and only 1 to 2 inches for fine or double-shredded mulch, which lets less oxygen through to the roots⁴. The depth field starts at 3 inches as an example; change it to suit your beds and material.

Bagged vs bulk mulch

Bags are sold by volume. The common North American retail size is 2 cu ft¹⁰; metric markets sell bark in sizes such as 60 L and 80 L¹¹¹². For larger areas, bulk mulch is sold by the cubic yard, 27 cu ft per yard¹. Switch between Bulk and Bags above to compare without changing your measurements.

Mulching around trees and plants

Keep mulch pulled back from trunks and stems rather than piled against them. Illinois says to keep mulch at least 4 inches from the trunk and that a 3-foot radius ring is the maximum for most trees³; Penn State puts the pull-back at 3 to 5 inches for young trees and 8 to 10 for mature ones so the root flare shows⁴. Mulch heaped against the trunk, the “volcano,” can lead to disease and insect problems at the base and eventually kill the plant⁵. For tree rings, choose Circle and enter the ring’s diameter.

Why mulch settles and breaks down

Organic mulch decomposes at a rate that depends on climate and material, and it needs replenishing as it breaks down; if mulch is already present, check the depth first and rake matted layers rather than piling on more³. This calculator doesn’t add an allowance for settling; decide your own margin.

Frequently asked questions

Sources & assumptions

• Volume = area × depth. Circles use π × r²; triangles use ½ × base × height.
• 1 cubic yard = 27 cubic feet; 1 cubic foot = 28.3168 liters; 1 m³ = 1.30795 cu yd.
• Bags are rounded up to whole bags from the exact, unrounded volume.
• Weights are estimates from loose, dry unit weights in the FHWA 1988 design-manual table: gravel 1.37, sand 1.30, topsoil 0.81 tons per cu yd. Moisture and stone type change them; your supplier’s figure replaces ours. Mulch weight isn’t estimated.
• No allowance is added for compaction, settling or waste, and no order size is suggested.
• Prices are only what you enter. CalcBrite doesn’t store or estimate local prices.
• Example depths are editable starting points taken from extension guidance cited in the sections above, not recommendations for your site.
• Metric bag sizes are examples of retail sizes (40–80 L); aggregates in metric markets are often sold by weight, so use Custom with the liters printed on the bag.

Sources

1. Guide to the SI, Appendix B.8: cubic yard, cubic foot and short ton factors, NIST Special Publication 811.
2. Table 6-12, Shrink/Swell Factors for Common Materials (loose and in-situ unit weights), Federal Highway Administration, Federal Lands Highway Project Development and Design Manual, Chapter 6 (September 1988); reproduced in Ohio DOT Technical Memo GE-65, Earthwork Factors (2008) — loose weights in lb per cubic yard: gravel, dry, average gradation 2,730 (wet 3,290); sand, dry 2,590 (wet 3,230); topsoil 1,620 (in place 2,430); earth loam, damp 2,360. Table notes a ±5% variation.
3. Proper Mulching Techniques (Tree Care Basics infosheet), University of Illinois Extension; Sarah Vogel & Jenny Lee; modified March 2024 — recommended depth 2 to 4 inches; composted materials 2–3 in, coarse mulches 3–4 in; keep mulch at least 4 inches from the trunk; a 3-foot radius ring is the maximum for most trees.
4. Mulching Landscape Trees, Penn State Extension; David R. Jackson; updated April 12, 2018 — 2 to 4 inches on well-drained soils, less on poorly drained; fine or double-shredded mulch 1 to 2 inches; keep mulch away from the trunk so the root flare shows; pull back 3–5 in from young trees, 8–10 in from mature trees.
5. Planting and Mulching Trees and Shrubs (fact sheet), University of New Hampshire Extension; Cathy Neal — two to three inches deep, out to the drip line; pull the mulch back a few inches from the trunk; “volcano mulching” can kill the plant.
6. Gravel Pathways in the Garden, University of California Master Gardeners, Contra Costa County; Earlene Millier; August 4, 2011, reissued March 2, 2020 — two inches is a practical minimum depth; allow four inches if thick stones or pavers are incorporated; river-run gravel never packs down, angular gravel packs to a nearly solid surface.
7. 10-Step Guide to Installing Pavers, hosted by Oregon State University Extension Service (2011 document) — excavation depth = base (4 to 6 inches) + sand bedding (1 inch) + paver thickness; base of crushed rock such as ¾-minus, compacted in layers (retail or trade listing).
8. Lawn Establishment, Penn State Extension; updated September 19, 2025 — a minimum of 4 to 6 inches (firmed or settled depth) of good-quality topsoil for good turf; till at least 4 inches.
9. Improving a Struggling Lawn and Repairing Damage, University of Maryland Extension; updated March 16, 2026 — about ¼ to ¾ inch of topsoil or compost can usually be put on turf without smothering the crown.
10. Timberline 2 cu. ft. Pine Bark Mini Nuggets Bagged Mulch, The Home Depot (retail listing) — example of the 2 cu ft bag size used as the default (retail or trade listing).
11. Rindenmulch grob 0-40 mm, 60 l, Hornbach (retail listing, Germany) — example of a 60 L metric bag (retail or trade listing).
12. Decorative garden bark, 1 × 80 litre bag, B&Q (retail listing, UK) — example of an 80 L metric bag (retail or trade listing).

Last reviewed:

October 2026

Last updated:

October 11, 2026

Calculator version:

1.0