A cubic yard of mulch is 27 cubic feet of volume. Spread at 3″ deep that covers 108 sq ft; at 2″ deep, 162 sq ft; at 4″ deep, 81 sq ft. By bag count: 13.5 bags at 2 cu ft per bag (retailers round up to 14), or 9 bags exactly at 3 cu ft.
The number that breaks first-year orders: 27 cubic feet of mulch fills 108 sq ft at 3″ deep, or 162 sq ft at 2″. Settling drops both numbers ~25% by mid-summer Year 1. Penn State Extension's landscape-tree mulching guidance calls out the 25-30% bulk-volume loss in the first 6 weeks. The geometric coverage assumes the mulch holds depth — the post-settling coverage is what you actually see by the time the summer listing photos go up.
Run any bed area through the mulch yardage calculator (it applies the 25% settling factor by default for fresh first-year apps and lets you toggle it off for refreshes on already-settled beds).
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Hi, I'm the SiteworkMath assistant. I answer questions about the calculators and guides on this site — concrete yardage, topsoil, mulch, tile, and decking material math. I'm not a structural engineer or a licensed contractor; I'm a calculator built around the math that James Wu — Chicago-area flipper — uses on his own jobs. For structural decisions (joist sizing, beam spans, footing depth in your soil + climate, anything that needs a permit) talk to a licensed structural engineer or your local building department.
How pros actually do this
The single number worth memorizing is 108 sq ft at 3″ deep, per cubic yard. From there everything else is one multiplication: doubling depth halves coverage, halving depth doubles it. A 4-bed front-yard landscaping plan that totals 240 sq ft at 3″ wants 2.22 yd³ geometric, 2.91 with the 5% waste cushion plus the 25% settling adjustment, rounded up to 3.0 yd³ practical. That math runs the same way whether the supplier delivers bulk or you cart bags out of a Menards.
Where the cubic-yard number bites first-year applications: the 25% settling cushion isn't optional. Fresh wood-chip mulch loses 25-30% of its bulk volume in the first 6 weeks as the chips compress, the bark edges crush, and any moisture gets driven out. Penn State Extension's mulching-landscape-trees page is the source for that figure; ANSI A300 (the formal arboriculture standard) backs the same 2-4″ depth range and adds the volcano-mulching prohibition that actually kills more trees than under-mulching does. A cubic yard ordered for a 108-sq-ft bed at 3″ that doesn't include the cushion looks correct for two weeks and thin for the rest of the season.
On the supply side: above 1 yd³, bulk delivery is almost always cheaper per yard than bagged. Below the typical 3 yd³ supplier minimum, bagged is usually the only practical call — most Chicago-suburb dispatchers won't deliver under 3 yd³ without a short-load fee that erases the savings. The awkward middle (1-3 yd³) is where access decides: if your alley or driveway can't take a delivery truck, bagged wins by default regardless of the per-yard math.
The cubic-yard math, line by line
1. A cubic yard is 27 cubic feet of volume.
1 yd × 1 yd × 1 yd, in feet, is 3 ft × 3 ft × 3 ft = 27 ft³. That definition is what every mulch supplier and bag manufacturer works back from. A bag labeled “2 cu ft” holds 2/27 of a cubic yard, or about 7.4%. A bag labeled “3 cu ft” holds 1/9.
2. Coverage = volume ÷ depth (depth in feet, not inches).
27 ft³ ÷ (3″/12) = 108 sq ft at 3″. 27 ÷ (2″/12) = 162 sq ft at 2″. 27 ÷ (4″/12) = 81 sq ft at 4″. The depth conversion is what trips most spreadsheet attempts — inches don't go straight into the divisor; they need to convert to feet first.
3. Bag count = 27 ÷ bag size in cubic feet.
27 ÷ 2 = 13.5 bags per cubic yard at the standard 2 cu ft retail size. Retailers round up to 14 because they can't sell half a bag. 27 ÷ 3 = 9 bags exactly at the larger 3 cu ft size. The half-bag is real waste at 2 cu ft — about 3.7% of the order.
4. Apply the 25% settling cushion for first-year apps.
The 108 sq ft figure is fresh-spread coverage. After 6 weeks of compression the same 27 ft³ of mulch covers about 81 sq ft of effective surface at the original 3″ depth — because the surface isn't at 3″ anymore, it's at roughly 2.25″. For first-year applications, multiply the exact yardage by 1.25 to land on a practical order that holds depth through summer. Refreshing an already-settled bed? Skip the cushion — the existing mulch has already taken the compression.
Coverage tables
Fresh-spread vs. post-settling coverage per cubic yard:
| Depth | Fresh-spread coverage | After-settling (Year 1, 25% loss) |
|---|---|---|
| 1″ | 324 sq ft | 243 sq ft |
| 2″ | 162 sq ft | 122 sq ft |
| 3″ | 108 sq ft | 81 sq ft |
| 4″ | 81 sq ft | 61 sq ft |
Bag-count breakdown for 1 cubic yard:
- 2 cu ft bags:
27 ÷ 2 = 13.5→ 14 bags retail (half-bag waste of ~3.7%) - 3 cu ft bags:
27 ÷ 3 = 9bags exactly (no rounding waste)
The 3 cu ft size is cheaper per cubic foot at most Chicago-suburb retailers and rounds clean to 9 bags — but it's heavier per bag (~60-70 lb vs. 40-45 lb) and not every store stocks it. The 2 cu ft size is the default because it's easier to handle out of a hatchback, not because the math works better.
Run the math yourself
Type your bed area below. The calculator's “Ornamental” preset uses 3″ by default; switch to “Vegetable” (1.5″), “Tree ring” (3″ at canopy edge with the trunk warning), or custom for other depths. The 25% settling cushion is on by default for first-year applications.
Where this number breaks down
A few traps that put a cubic-yard order on the wrong side of the bed:
- Fresh-spread coverage isn't what you actually get by mid-summer. The 108 sq ft figure at 3″ is geometric — it assumes the mulch holds depth. By week 6 the surface has compacted ~25% per Penn State Extension. First-year applications need the 1.25 multiplier baked in or the bed looks thin by July.
- Bag-label coverage assumes settled depth, not fresh-spread. Most 2 cu ft bag labels say “covers 8 sq ft at 3 inches” — which is the post-settling math, not the spread-time math. Buying to the bag-label number for a fresh first-year app is the same trap as buying to the geometric yardage and skipping the cushion.
- Different mulch types pack different. Fine shredded bark and dyed mulch pack denser than coarse wood chips — fine covers ~10% more area per cubic yard at the same depth but settles faster, so the post-settling math comes out roughly even. Coarse bark nuggets are the outlier: they cover slightly less, settle less, and last longer.
- Bulk delivery sometimes runs heavier than 27 ft³ when wet. Wet wood-chip mulch off a fresh delivery truck can come in a few percent over the labeled 27 ft³ — extra moisture weight distorts the loose-bulk volume estimate the supplier's front-end loader uses. Wet weight isn't the same as dry volume; the labeled cubic yard is supposed to be dry but isn't always.
- Volcano-mulching the trees in a 1-yard order is the trap that kills the bed. ANSI A300 and Penn State Extension both call for mulch pulled 3-10″ away from the trunk depending on tree age. A cubic yard that goes down evenly is fine; a cubic yard that gets piled in cones against tree trunks suffocates bark and rots the cambium. Most newly-mulched trees that die do so from this — not from under-mulching.
Frequently asked
How many square feet does a cubic yard of mulch cover at 3″?
108 sq ft fresh-spread. Math is 27 ft³ ÷ (3″/12) = 108 sq ft. By mid-summer of Year 1 that surface compacts to roughly 81 sq ft of effective coverage, because Penn State Extension's wood-chip mulch loses ~25% of its bulk volume in the first 6 weeks. Order to the fresh-spread number for first-year apps; refreshes off an already-settled bed match the geometric coverage one-to-one.
How many bags equal one cubic yard?
13.5 bags at 2 cu ft per bag (most common retail size); 9 bags exactly at 3 cu ft. Retailers can't sell half-bags, so a 2 cu ft cubic-yard order rounds up to 14 bags. Quick math is 27 ÷ bag-size in cubic feet. The 14-bag round-up is real waste — a half-bag's worth of mulch — but you can't fix it without splitting the order across bag sizes, which most stores don't price symmetrically.
How long does fresh mulch last before it settles?
About 6 weeks until it's fully compressed, per Penn State Extension's wood-chip-mulch observations. The volume loss is 25-30% over that window — fastest in the first 2 weeks, then slower. After 6 weeks the surface is stable until the seasonal decomposition cycle takes over (18-24 months for natural wood chip; 24-36 for dyed). The 25% factor isn't year-over-year decay, it's first-spread compression.
Does the depth I spread change how many cubic yards I need?
Linearly. A cubic yard at 1″ deep covers 324 sq ft; at 2″ it's 162; at 3″ it's 108; at 4″ it's 81. Double the depth, halve the coverage. The Penn State Extension 2-4″ range covers most landscape uses — vegetables want 1.5-2″, ornamentals want 3″, tree rings want 3″ at the canopy edge with the trunk pulled back to bare ground per ANSI A300.
Why is the post-settling coverage 25% less?
Fresh wood-chip mulch is loose — air pockets between chips, bark edges that haven't compressed, dyed bark that hasn't shed water and locked in. Penn State Extension's landscape-tree mulching guidance notes the 25-30% volume loss in the first 6 weeks as the material settles to its true packed density. The geometric coverage number (108 sq ft at 3″) assumes you spread to 3″ AND it stays there — the post-settling number is what the bed actually looks like by the time the listing photos go up.
Should I order an extra cubic yard for the settling cushion?
For first-year applications, yes — but the cleaner math is to multiply your exact yardage by 1.25 rather than always adding a full extra yard. A 2 yd³ bed becomes 2.5 yd³ practical; a 4 yd³ bed becomes 5 yd³. SiteworkMath's mulch calculator handles the multiplier automatically. For refreshes off an existing settled bed, skip the cushion entirely — the existing mulch has already taken the compression, and a fresh top layer just brings the surface back to spec.
Related guides
- How much mulch do I need for my garden bed →
- How much mulch is in a yard →
- Mulch: square yard vs cubic yard →
- Mulch calculator (cluster anchor) →
Once the cubic-yard coverage is dialed, the next decision is usually scaling it to a real bed — area in, yardage out, with the cushion baked in. How much mulch do I need for my garden bed covers it.
By James Wu. Volume math (27 ft³ per yd³, coverage = volume ÷ depth) is site arithmetic, formulas shown above. Mulch depth recommendations + the 25% bulk-volume settling figure from Penn State Extension — Mulching Landscape Trees. Arboriculture standard via ANSI A300 (Tree Care Industry Association) for the formal 2-4″ depth specification + the volcano-mulching prohibition. Tree-protection cross-check from Iowa State Extension — Mulch Depth Around Trees and Shrubs. Engine logic in lib/sitework/mulch.ts. Not arboriculture advice — for tree-care decisions specific to your trees, work with an ISA-certified arborist. Full methodology.