Cubic Yards Explained: Cubic Feet, Coverage by Depth, and Cost

A cubic yard is 27 cubic feet — enough material to cover 108 square feet at the standard 3-inch depth used for mulch, gravel, and topsoil, or 81 square feet at 4 inches.

Every bulk landscaping and concrete material — mulch, gravel, topsoil, sand, concrete — is priced and delivered by the cubic yard, but the measurements a homeowner actually takes come out in feet and inches. Converting between the two is the one calculation every volume estimate on this site runs underneath, so it’s worth understanding once instead of re-deriving it per project.

Why 27

A cubic yard is a cube 3 feet on each side: 3 × 3 × 3 = 27 cubic feet. That single fact is the whole conversion — everything below is that number applied to a specific area and depth. It’s also why every volume calculator here — mulch, gravel, topsoil, concrete slabs — divides by 27 as its final step: multiply length by width by depth (all in feet) to get cubic feet, then divide by 27 to get the cubic yards a supplier actually sells.

Coverage by depth: how far one cubic yard goes

Coverage is just that 27-cubic-foot volume spread thin. Divide 324 (27 cubic feet × 12 inches per foot) by the depth in inches to get square feet covered by one cubic yard:

Depth	Coverage per cubic yard
1 in	324 sq ft
1.5 in	216 sq ft
2 in	162 sq ft
3 in	108 sq ft
4 in	81 sq ft
6 in	54 sq ft
12 in (1 ft)	27 sq ft

The 2–4 inch rows cover what most homeowners are estimating: 2 inches is a light mulch refresh or a decorative gravel topping, 3 inches is the standard mulch and path-gravel depth, and 4 inches is a typical concrete slab, gravel driveway surface, or new-lawn topsoil layer. Go deeper than that — a 10–12 inch raised-bed fill, for instance — and coverage per yard drops fast, which is why raised beds eat through topsoil so much quicker than a flat bed of the same footprint.

The formula, worked through

cubic yards = (length × width × depth in inches) ÷ 324

A 10 × 20 ft area at 3 inches deep: 10 × 20 × 3 = 600, and 600 ÷ 324 ≈ 1.85 cubic yards. That’s the exact math behind a 10 × 20 ft bed on the mulch calculator and the gravel calculator at their default 3-inch depth — the geometry is identical no matter which material fills it. Add 5–10% waste on top for settling, uneven edges, and spillage before rounding up to a shoppable bag count or bulk order.

Bags per cubic yard, by material

Bagged sizes vary by product, so “how many bags in a yard” has a different answer for each one:

Material	Bag size	Bags per cubic yard
Mulch	2 cu ft	13.5
Gravel	0.5 cu ft	54
Topsoil	40 lb (≈0.75 cu ft)	36
Concrete mix	80 lb (≈0.6 cu ft)	45

Each figure is 27 divided by the bag’s cubic-foot yield — check the label before assuming a number, since off-brand bags vary. Past roughly 1–3 cubic yards (the exact threshold depends on the material and local delivery fees), bulk almost always beats stacking that many bags, on both price and labor.

What a cubic yard costs

US ballpark ranges, delivered in bulk, as of 2026-07 — actual pricing depends heavily on region, material grade, and delivery distance:

• Mulch: roughly $25–$50 per cubic yard in bulk, more for cedar or dyed grades. See how much mulch do I need for the bagged-vs-bulk breakeven.
• Gravel: sold by the ton, not the yard — about $50–$75 per ton, which works out to roughly $70–$105 per cubic-yard equivalent at gravel’s ~1.4 tons-per-yard density. See how much gravel do I need for the full ton conversion.
• Topsoil: roughly $15–$40 per cubic yard in bulk for standard fill-grade soil, before delivery.
• Ready-mix concrete: roughly $150–$200 per cubic yard delivered by truck; bagged mix runs meaningfully more per yard-equivalent and only makes sense under about 1 cubic yard. See how much concrete do I need for the bag-vs-truck math.

Delivery minimums are the detail that catches people off guard — most bulk suppliers won’t deliver less than 1–3 cubic yards (5+ tons for gravel), so a small job sometimes prices out cheaper in bags even where bulk looks cheaper per unit.

Run your own numbers

Manual conversion works fine for a single estimate, but it’s easy to drop a decimal or mix up feet and inches under real measuring conditions. The mulch, gravel, topsoil, concrete slab, and concrete bags calculators all take length, width, and depth directly and return both the cubic-yard total and a rounded-up purchase count, so there’s no manual division required.

Updated: 2026-07-15