Why bulk volume is measured in cubic yards
A cubic yard is the unit that a truck was built around. A standard ready-mix drum carries eight to eleven cubic yards, a tandem dump truck hauls roughly ten to fourteen, and a yard of most aggregates weighs somewhere between 2,000 and 3,000 pounds — comfortably inside what a small truck can legally carry. That is why concrete, gravel, topsoil, mulch, sand and fill are all quoted per cubic yard in North America, while the rest of the world quotes the same materials per cubic meter, which is 1.31 times bigger.
The conversion you actually use on site is not between yards and meters, though. It is between the units you measured in and the unit you order in. You measure a driveway in feet and its thickness in inches, and you have to buy it in cubic yards. That mismatch — two feet dimensions, one inch dimension, one yard answer — is where nearly every ordering error comes from, because the two divisions involved, 12 and 27, are easy to apply in the wrong order or to forget entirely.
The relationships themselves are simple and exact. A yard is three feet, so a cubic yard is 3³ = 27 cubic feet. A yard is 0.9144 m by the 1959 definition, so a cubic yard is 0.9144³ = 0.764554857984 m³, with no rounding. Everything else on this page comes from those two facts plus the definition of the US liquid gallon as 231 cubic inches.
The formula, and why the 12 comes before the 27
Working a volume from site dimensions is three operations in a fixed order. First convert the odd dimension — the thickness — into the same unit as the others. Slab thickness is specified in inches, so divide by 12 to get feet. Then multiply the three feet dimensions to get cubic feet. Finally divide by 27 to reach cubic yards.
Order matters only in the sense that both divisions must happen exactly once. A four-inch slab is 0.3333 ft thick, not 4 ft and not 48 ft; skipping the 12 overstates the order by a factor of twelve, which is the single most expensive arithmetic error in residential concrete. Dividing by 27 twice, or by 3 instead of 27, is the second.
For the metric route the arithmetic is friendlier because the units nest by powers of ten. Measure in meters, multiply the three dimensions, and you have cubic meters directly. A liter is a thousandth of a cubic meter, so the same number shifted three places is liters. That is why bagged garden products in metric markets are sold in liters — a 50 L bag is 0.05 m³, and twenty of them make a cubic meter.
Gallons come from a different definition again. The US liquid gallon is exactly 231 cubic inches, so a cubic foot (1,728 cubic inches) holds 1728/231 = 7.4805 gallons, and a cubic yard holds 27 × 7.4805 = 201.97 gallons. Use these when you are filling something rather than placing something — see the pool volume calculator and the gallons to liters calculator.
Worked example: a 20 ft by 12 ft patio slab, 4 inches thick
You are pouring a rectangular patio 20 feet long, 12 feet wide, at the standard residential slab thickness of 4 inches.
- Thickness in feet. 4 ÷ 12 = 0.3333 ft.
- Volume in cubic feet. 20 × 12 × 0.3333 = 80 ft³. (Exactly 80, because 20 × 12 = 240 and 240 ÷ 3 = 80.)
- Volume in cubic yards. 80 ÷ 27 = 2.963 yd³.
- Volume in cubic meters. 2.963 × 0.764554857984 = 2.2653 m³. Check it the other way: 80 × 0.028316846592 = 2.2653 m³.
- What to order. Ready-mix is sold in quarter-yard increments and you need an allowance for subgrade irregularity and spillage. At a 10% allowance, 2.963 × 1.10 = 3.26 yd³, so you would order 3.25 or 3.5 yards.
Change only the thickness to 6 inches and the volume becomes 20 × 12 × 0.5 = 120 ft³ = 4.444 yd³. Fifty per cent more thickness is fifty per cent more concrete, because volume is linear in each dimension separately.
How to read the result before you order
The calculator gives you neat volume. What you buy is neat volume plus an allowance, and the size of that allowance depends on what the material is doing. For concrete against formed edges on a prepared base, 5–10% covers subgrade variation and waste. For concrete against an unformed trench or a rough subgrade, allow more, because every low spot in the base is extra concrete that has to be paid for. For mulch, topsoil and gravel, the loose delivered volume settles once placed and compacted, so the delivered yardage should exceed the calculated in-place volume — ask your supplier for the compaction factor of the specific material rather than assuming one.
Watch the supplier's minimum. Most ready-mix plants set a minimum load of one to three yards and add a short-load charge below it, which is why the calculator flags volumes under half a yard: at that size bagged mix is often cheaper, and the concrete bag calculator converts the volume into 60 lb and 80 lb bags.
Finally, keep volume and weight separate in your head. A cubic yard is a volume, and the weight it corresponds to depends entirely on the material: dry sand, wet topsoil and crushed limestone all occupy a yard and none of them weighs the same. Haulage limits, bag counts and delivery fees are usually driven by weight, so convert with a density — the gravel tonnage calculator does this for aggregates.
Exact bulk-volume conversion reference
| One unit of | Cubic feet | Cubic yards | Cubic meters | Liters | US gallons |
|---|---|---|---|---|---|
| Cubic foot | 1 | 0.037037 | 0.028316847 | 28.3168 | 7.48052 |
| Cubic yard | 27 | 1 | 0.764554858 | 764.555 | 201.974 |
| Cubic meter | 35.314667 | 1.3079506 | 1 | 1,000 | 264.172 |
| Liter | 0.0353147 | 0.00130795 | 0.001 | 1 | 0.264172 |
| US gallon | 0.133681 | 0.00495113 | 0.003785412 | 3.785412 | 1 |
| Cubic inch | 0.000578704 | 0.0000214335 | 0.0000163871 | 0.0163871 | 0.004329 |
Read across: one cubic yard is 27 cubic feet, 0.7646 cubic meters and 201.974 US gallons.
Ordering mistakes this calculator is meant to prevent
- Leaving the thickness in inches. A 4 in slab entered as 4 ft overstates the pour twelve-fold. Always divide the inch dimension by 12 first, or use the depth field, which does it for you.
- Dividing by 3 instead of 27. A yard is three feet linearly, but volume scales by the cube, so the divisor is 3³. Dividing by 3 orders nine times too much material.
- Confusing cubic yards with square yards. Flooring, carpet and turf are sold by area; concrete, gravel and soil by volume. If your quantity has no thickness in it, you are working in square units and this calculator is the wrong tool — use the square feet to square meters calculator.
- Ignoring waste and subgrade variation. A 4 in slab poured on a base that dips half an inch in places is not a 4 in slab. On residential work an allowance of 5–10% is normal practice; the exact figure depends on how well the base was prepared.
- Assuming loose and compacted volumes are equal. Aggregates and soils occupy more space in the truck than in the trench. The delivered volume you need is the in-place volume divided by the material's compaction factor, which your supplier can give you.
- Treating an imperial gallon as a US gallon. The imperial gallon is 4.54609 L against the US gallon's 3.785412 L, a 20.9% difference. The gallons output here is the US liquid gallon.
Related volume and material tools
This page converts a volume. Turning that volume into an order usually needs one more step, and which step depends on the material. For a slab, footing or column, the geometry is worth doing properly — the concrete slab calculator handles thickened edges and waste allowance, and the concrete footing calculator handles continuous footings. For landscaping, the mulch cubic yards calculator works from bed area and depth and reports the bagged equivalent.
Where the constraint is weight rather than space — a haulage limit, a delivery fee, a floor loading — you need a density as well as a volume. Aggregate densities vary by rock type and moisture, so use a supplier figure rather than a generic one.
If your volume is a liquid rather than a solid, switch families. Tanks, pools and chemical dosing are quoted in gallons and liters, and the gallons to liters calculator and the pipe volume calculator are built around those units. The underlying arithmetic is identical; only the conventional units differ.