Concrete & Material Calculator

Concrete, and every other material sold by volume

Most people arrive here for concrete — how many bags for a slab, a footing or a set of posts — and the answer is below. The same three steps cover gravel, mulch, topsoil and sand too: work out the area, multiply by the depth to get a volume, then convert that volume into whatever unit the supplier sells in.

cubic yards = length (ft) × width (ft) × depth (in) ÷ 12 ÷ 27

The two constants are the ones people forget. Depth is almost always given in inches while length and width are in feet, so it has to be divided by 12 first. And there are 27 cubic feet in a cubic yard, not 3 — a yard is three feet in each of three dimensions.

Concrete: how many bags per cubic yard

Bagged concrete is sold by weight, and each bag yields a fixed volume of mixed concrete. Yields from the QUIKRETE Concrete Mix No. 1101 product data sheet, checked 17 September 2026. A cubic yard is 27 cubic feet, so the bag counts follow from the yield.

* Interpolated from the published 40, 60 and 80 lb yields rather than listed separately.

The crossover point is worth knowing before you load a trolley. At roughly one cubic yard — 45 bags of 80 lb, about 3,600 lb of material — ready-mix delivery is usually cheaper and always less work. Below about half a yard, bags win.

Strength arrives on a schedule, and it is slower than people expect. A standard mix reaches about 2,500 psi at seven days and 4,000 psi at twenty-eight — so a week in, a slab is only 63% of the way there. Foot traffic is usually fine after a day or two, but a slab meant to carry a vehicle wants the full twenty-eight days. Concrete cures rather than dries; keeping it damp for the first week makes it stronger, not weaker.

Worked example: a 10 × 10 patio slab

That is already past the ready-mix crossover. Ordering 1.5 yards delivered beats carrying 62 bags.

Converting cubic yards to tons

Suppliers quote gravel, sand, and topsoil by the ton as often as by the yard, and the conversion needs the material's density — there is no universal factor:

The spread is enormous — a cubic yard of concrete weighs five times what a cubic yard of mulch does. These are dry loose values; wet material can weigh 10–20% more, which matters when a delivery is priced by weight and when you are checking a trailer's load rating.

Mulch, bark, and pine straw coverage

Mulch is sold in 2 cubic foot bags, which gives 13.5 bags per cubic yard. A standard pallet holds about 65 bags, or roughly 4.8 cubic yards.

Two to three inches is the usual recommendation — enough to suppress weeds and hold moisture, without smothering roots. A bale of pine straw covers roughly 35–50 sq ft at that depth, so it is priced per bale rather than by volume.

Depth by project

Why the waste allowance matters

Order the exact calculated figure and you will come up short. Ground is never perfectly level, sub-base settles, material compacts, and some is always lost in handling. Add 5–10% — the higher end for concrete, where running out mid-pour means a cold joint and a visible seam that cannot be fixed afterwards.

Being over on bulk material is cheap. Being under on a concrete pour is not.

For the plain geometry, the area calculator handles irregular shapes and the volume calculator covers cylinders and spheres. To convert between length units first, use the length converter.