Gravel & Mulch Calculator

How the math works

Bulk landscape material is sold by volume — the cubic yard — so every estimate starts with the same three numbers: the area of your bed, the depth you want, and a density to turn volume into the tons a supplier weighs out.

Area is plain geometry. A rectangular bed is length × width; a round bed is π × radius². Multiply the area (in square feet) by your depth in feet — that's the depth in inches divided by 12 — and you have cubic feet. Divide by 27 and you have cubic yards, the unit the yard sells in. For gravel, crushed stone, river rock, sand, and topsoil, the calculator also multiplies cubic yards by a published density to give you weight in tons, because aggregate is often priced and loaded by the ton.

Densities, and why mulch is different

Typical gravel and crushed stone run about 1.4 tons per cubic yard, sand about 1.35, and dry topsoil about 1.1. Mulch is the odd one out: it's so light (around half a ton per yard) and so variable by type and moisture that it's almost always sold and bought by volume, not weight — so the calculator reports cubic yards and bags for mulch and skips the tonnage. These densities are dry industry averages; wet material weighs noticeably more, so confirm with your supplier before you hitch up a trailer.

Bags vs. bulk — the real decision

The crossover is around three cubic yards. Bagged mulch is usually 2 cubic feet per bag, so a single cubic yard is roughly 14 bags — and at a few cubic yards you're hauling, lifting, and opening dozens of them at a per-cubic-foot price several times the bulk rate. Bulk delivery wins decisively above about 3 yards. Below that, bags can be the smart call: there's no delivery minimum, no surcharge, and you only buy what fits in the car. The calculator flags which side of the line your job lands on.

How deep, and the coverage number

Depth is where people go wrong. Gravel thinner than 2 inches lets the base show through and shifts underfoot; driveways want 3-4 inches, usually over a separate compacted sub-base. Mulch is the opposite problem — pile it past 3-4 inches and you trap moisture against stems and can suffocate roots, so 2-3 inches is the sweet spot for most beds. The calculator also shows how many square feet one cubic yard covers at your chosen depth (324 ÷ depth in inches), a handy sanity check: a yard covers about 162 sq ft at 2 inches, 108 sq ft at 3 inches.

A worked driveway example

Say you're topping a gravel driveway 40 feet long and 12 feet wide with a fresh 4-inch layer. The area is 480 square feet. Four inches is a third of a foot, so the volume is 480 × 0.333 = 160 cubic feet, which is 160 ÷ 27 ≈ 5.9 cubic yards. At gravel's 1.4 tons per yard that's about 8.3 tons — well past the bag-versus-bulk line, so you'd order a bulk load by the ton and have it dumped, not buy a hundred-plus bags. If you were instead mulching a 200-square-foot bed at 3 inches, the same arithmetic gives 50 cubic feet, under 2 cubic yards, or about 25 two-cubic-foot bags — a borderline case where bags are still manageable if bulk delivery carries a minimum.

One more thing the raw volume doesn't capture: compaction. Driveway base material is meant to be tamped down, and aggregate can settle 10-20% once compacted and driven on. If you're building up a base rather than just refreshing the surface, order a little extra — running short means a second delivery fee for a few missing cubic feet.

When this calculator is the wrong tool

This covers loose material spread over an area at a roughly uniform depth — beds, paths, driveways, and fill. It doesn't size a structural driveway base (that's an engineered layer cake of sub-base and surface), and it doesn't account for heavy compaction, which can settle aggregate 10-20% and means you should order a little extra. For retaining-wall backfill or drainage gravel behind a wall, follow the wall system's spec.

Material densities are industry averages (tons per cubic yard) and vary by moisture and source; confirm with your supplier. Volume is plain math.