Mulch Calculator
How much mulch to buy, in cubic yards and in 2 or 3 cu ft bags, for one bed or several — rectangles, tree rings or a square footage you already know — with the depth extension services recommend for each kind of mulch.
The short version: cubic yards = square feet × depth (in) ÷ 324. Most wood mulch goes on 2–3 inches deep. A 20 × 4 ft bed at 3 inches needs 0.75 yd³ — 10 bags of 2 cu ft or 7 of 3 cu ft.
Recommended: 2–3 in. Clemson: many wood and bark mulches are fine-textured and should be no more than 2–3 in deep. UF: no more than 3 in, because too much can divert rain from the roots.
Enter the depth you want after it settles. Fresh mulch settles and breaks down; add 10–20% if you're spreading it fluffy, or plan to top up next year.
You need
0.75 cubic yards of shredded mulch
20 cu ft · 80 sq ft at 3 in
10
2 cu ft bags
7
3 cu ft bags
Beds against the house: keep mulch 6–12 in back from the walls (Clemson) and under 2 in deep within a foot of the foundation (UF/IFAS), never touching siding, and don't use mulch to build up the grade — why.
Show the math
- Beds: 80 sq ft in all
- 80 × (3 ÷ 12) = 20 cu ft ÷ 27 = 0.74 yd³
- 20 ÷ 2 = 10 → 10 bags
- 20 ÷ 3 = 6.67 → 7 bags
How the calculator works
Each bed is converted to square feet — length × width, or π × radius² for a ring — and added up. That total × depth ÷ 12 is cubic feet; ÷ 27 is cubic yards. Clemson's and UF/IFAS's extension fact sheets give the same rule of thumb: one cubic yard covers 324 sq ft one inch deep. Bags are the cubic feet ÷ the bag size, rounded up.
The depth you enter is the depth you want once it has settled. Mulch doesn't compact the way gravel does, but it breaks down: in UF/IFAS's two-year test, pine straw was almost gone while pine bark and cypress kept about two-thirds of their depth. The optional extra covers spreading it fluffy; most beds simply get topped up each spring.
How deep, by mulch type
| Mulch | Depth | Why |
|---|---|---|
| Shredded wood or bark (fine) | 2–3 in | Clemson: many wood and bark mulches are fine-textured and should be no more than 2–3 in deep. UF: no more than 3 in, because too much can divert rain from the roots. |
| Pine bark nuggets (coarse) | 3–4 in | Clemson: coarse mulches such as pine bark nuggets let air move through and can be as deep as 4 in. Nuggets float, so keep them out of rain gardens and swales. |
| Pine straw / needles | 2–3 in | Clemson: pine needles 2–3 in. It breaks down fastest — in UF's two-year test pine straw was almost gone, so expect to top it up yearly. |
| Shredded leaves or grass clippings | 1–2 in | Clemson: grass clippings and shredded leaves no more than 2 in deep. |
| Rain garden (double-shredded hardwood) | 2–4 in | Wisconsin DNR: about 3 in of double-shredded mulch. University of Maine: 3–4 in, and bark chips don't work because they float away. Vermont: 2–3 in. |
Stone or rock mulch is a different calculation — Clemson says a 1-inch layer of small rock gives good weed control — and it's sold by the ton, so use the gravel calculator.
Mulch coverage table
Cubic yards, and 2 / 3 cu ft bags, for common bed sizes and depths. No settling extra added.
| Bed area | 2 in deep | 3 in deep | 4 in deep |
|---|---|---|---|
| 50 sq ft | 0.31 yd³ · 5 / 3 bags | 0.47 yd³ · 7 / 5 bags | 0.62 yd³ · 9 / 6 bags |
| 100 sq ft | 0.62 yd³ · 9 / 6 bags | 0.93 yd³ · 13 / 9 bags | 1.2 yd³ · 17 / 12 bags |
| 200 sq ft | 1.2 yd³ · 17 / 12 bags | 1.9 yd³ · 25 / 17 bags | 2.5 yd³ · 34 / 23 bags |
| 300 sq ft | 1.9 yd³ · 25 / 17 bags | 2.8 yd³ · 38 / 25 bags | 3.7 yd³ · 50 / 34 bags |
| 500 sq ft | 3.1 yd³ · 42 / 28 bags | 4.6 yd³ · 63 / 42 bags | 6.2 yd³ · 84 / 56 bags |
| 1,000 sq ft | 6.2 yd³ · 84 / 56 bags | 9.3 yd³ · 125 / 84 bags | 12.3 yd³ · 167 / 112 bags |
Mulch and drainage around the house
Mulch beds usually sit right against the foundation, which is exactly where water needs to run away from the house. A few rules keep the bed from working against the grade:
- Keep it back from the walls. Clemson Extension: keep mulch 6–12 inches from building walls. UF/IFAS: no more than a thin layer, under 2 inches, within 12 inches of the foundation.
- Never against siding or trim. University of Kentucky entomologists say mulch should never contact wood siding or door and window frames, which should sit at least 6 inches above the ground. The building code says the same for the foundation: at least 6 inches showing above finished grade, 4 inches with brick or stone veneer (IRC R404.1.6), and stucco weep screeds at least 4 inches above the earth (R703.7.2.1). Mulch piled over that line hides it and holds water against the wall.
- Don't use mulch to build up the grade. The ground should fall 6 inches in the first 10 feet from the house (IRC R401.3). Mulch on top of a level or back-sloping bed doesn't fix that — it soaks up water and lets it through to the soil beside the wall. Shape the soil first; the topsoil calculator's regrading mode works out the fill, then mulch over it.
- Mind the downspouts. A downspout emptying into a mulch bed scours it and soaks the soil at the foundation. Extend it past the bed, or end it in stone — see downspout drainage problems.
- Keep the inspection gap visible. UF/IFAS notes the code's 6-inch inspection gap, and that mulch deeper than 4–6 inches obscures it, which is where termite tubes would show.
Mulch, runoff and rain gardens
A thin layer of mulch helps water soak in. Clemson Extension says mulch prevents crusting of the soil surface, improving how water is absorbed and moves into the soil, and stops rain splashing soil out of beds. Too much works the other way: UF/IFAS warns that more than 3 inches can divert rain and irrigation away from roots.
Where water flows or ponds, the type matters more than the depth. University of Maine Extension says bark chips don't work in rain gardens because they float away; the Wisconsin DNR rain garden manual uses about 3 inches of double-shredded mulch, which knits together. The same logic applies in a swale or along any path water takes in a storm — loose nuggets end up at the low end, or in the drain. A rain garden filled for its first few years with mulch and young plants needs a top-up each spring until the plants fill in; the rain garden calculator sizes the garden and its mulch layer.
Worked example: a 150 sq ft rain garden at 3 inches of double-shredded mulch takes 37.5 cu ft — 1.4 yd³, or 19 bags of 2 cu ft.
More worked examples
Three beds: 30 × 5 ft, 12 × 4 ft and a 6 ft tree ring, at 3 inches
150 + 48 + 28.3 = 226.3 sq ft × 0.25 ft = 56.6 cu ft. That's 2.1 cubic yards, 29 bags of 2 cu ft or 19 of 3 cu ft — a size where bulk delivery is usually worth pricing.
Topping up an existing bed
Measure what's there first. If shredded mulch has settled to 1 inch and you want 3, enter 2 inches. Adding a fresh full layer every year is how beds end up 6 inches deep and burying the bottom of the siding.
What this doesn't tell you
- Prices — bagged and bulk mulch vary too much by region to publish. Compare the bag count × price with a bulk quote including delivery.
- Whether a wet bed needs drainage rather than more mulch. Water standing in a bed after rain is a grade or soil problem.
- Pine straw bales and rubber mulch, which are sold by coverage figures that vary by product; check the label.
Frequently asked questions
How much mulch do I need?
How many yards of mulch do I need?
How deep should mulch be?
How many bags of mulch are in a yard?
How much does a bag of mulch cover?
How far should mulch be from the house?
Does mulch cause termites?
What mulch is best for a rain garden?
How much mulch for a tree ring?
Sources
- Clemson Cooperative Extension, Home & Garden Information Center — Mulch (HGIC fact sheet): depths by type, 2–3 in from stems, 6–12 in from walls, 324 sq ft per yd³ at 1 in
- UF/IFAS Gardening Solutions — Mulch: 2–3 in around established plants, no more than 3 in, about 1 ft from the base of trees
- University of Maine Cooperative Extension — Bulletin 2702, rain gardens: 3–4 in of mulch; bark chips float away
- UF/IFAS (Duryea & Minogue) — FR052, how long mulches last: pine straw almost gone after two years; pine bark and cypress kept about two-thirds of their depth
- Wisconsin Department of Natural Resources — Rain Gardens: A How-To Manual — about 3 in of double-shredded mulch
- Vermont Department of Environmental Conservation / UVM — Vermont Rain Garden Manual: a 2–3 in layer of mulch
- UF/IFAS EDIS (Oi & Wheeler) — IN651, mulch and termites: a thin layer (under 2 in) within 12 in of the foundation; the code's 6 in inspection gap
- University of Kentucky Entomology — EF605, termites: mulch sparingly and never against wood siding or door and window frames; wood at least 6 in above ground
- International Code Council, International Residential Code (2021): R401.3 Drainage; R404.1.6 Height above finished grade; R703.7.2.1 Weep screeds. Your local adoption may differ.
Every constant the site's tools use is listed on how we calculate.
Related
- Rain gardens — where roof water soaks in, and how to build one
- Gravel calculator — stone mulch, paths and drainage stone
- Topsoil & fill dirt calculator — soil for new beds and regrading away from the house
- Water pooling near the foundation — grade, downspouts and what to check first