Area and depth in — cubic yards, tons, bags and cost out, using the real density of the material you actually ordered rather than a generic average.
2–3 in for a decorative bed · 4 in for a walkway · 6–8 in for a driveway base · 3 in for mulch.
Density varies with moisture and how tightly the load is packed — treat the weight as an estimate and round your order up.
%
Loose aggregate settles when compacted. 10% for a decorative layer, 15–20% for a compacted base.
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The calculation
Area × depth = volume, and everything else is unit conversion. The one step people get wrong is the depth: it is given in inches while the area is in feet, so it must be divided by 12 before multiplying. A 12 × 30 ft area at 4 in deep is 360 ft² × 0.333 ft = 120 ft³, and since a cubic yard is 27 ft³, that is 4.44 cubic yards.
Yards, tons and why suppliers use both
Bulk aggregate is sold by volume (the cubic yard) or by weight (the ton), and which you get depends on the yard. Converting between them needs the density of that specific material, which is why one blanket figure will not do:
Material
lb per ft³
Tons per yd³
Crusher run / road base
115
1.55
Gravel, ¾ in crushed
105
1.42
Pea gravel, river rock, sand
100
1.35
Topsoil
80
1.08
Compost
45
0.61
Bark mulch
20
0.27
The spread is the point: a cubic yard of road base weighs nearly six times what a cubic yard of bark mulch does. Ordering "two tons" of mulch and "two tons" of gravel gets you wildly different amounts of coverage.
Recommended depths
Decorative beds and borders — 2 to 3 in
Mulch around plants — 3 in, kept clear of stems
Footpaths — 3 to 4 in over a compacted base
Driveways — 4 in of surface stone over 4 to 6 in of compacted base
Under a paver or shed base — 4 to 6 in of compacted crusher run
Delivery is usually the largest single line on a small aggregate order, so a second trip for the last half yard costs more than the material itself. Round up to the next half yard, and if you are close to a full truckload, ask what the price break is — many suppliers charge nearly the same for 8 yards as for 5 once haulage is included.
Compaction is not waste
Loose aggregate arrives fluffed up and settles as it is raked, walked on and compacted — typically 10 to 20% depending on the material and how hard you tamp it. That is not spillage, it is volume that genuinely disappears into the finished depth, and it is why the allowance above is on by default. For a compacted driveway base use 20%; for mulch that will never be compacted, 5% is plenty.
Bagged material makes sense only for small jobs — under about a cubic yard, roughly 40 bags. Beyond that, bulk delivery is usually less than half the price per yard.
Allow 4 inches of surface gravel over a 4 to 6 inch compacted base. A 12 × 40 ft driveway at 4 inches is about 5.9 cubic yards, or roughly 8.4 tons of ¾ inch crushed gravel — plus the base layer underneath.
How many square feet does a yard of gravel cover?
One cubic yard covers about 162 ft² at 2 in deep, 108 ft² at 3 in, 81 ft² at 4 in, and 54 ft² at 6 in. Double the depth and you halve the coverage.
How many tons is a cubic yard of gravel?
About 1.4 tons for ¾ inch crushed gravel, 1.35 for pea gravel and sand, and 1.5 to 1.6 for crusher run. Lighter materials differ sharply — a yard of bark mulch is only around a quarter of a ton.
How many bags of mulch make a cubic yard?
Thirteen and a half of the standard 2 ft³ bags, since a cubic yard is 27 ft³. Bulk delivery is normally far cheaper than bags once you need more than about a yard.
How deep should mulch be?
Two to three inches is right for most beds. Deeper than four inches restricts water and air reaching the roots, and mulch piled against trunks or stems traps moisture and invites rot — always leave a gap at the base of the plant.