Cubic Yard Calculator
Volume of slabs, holes, footings and cylinders in cubic yards, feet and metres, several pieces added, with the depth in inches.
Quick answer: cubic yards in a slab
| Slab | 4 in. thick | 6 in. thick | 4 in., +10 % |
|---|---|---|---|
| 10 × 10 ft | 1.23 | 1.85 | 1.36 |
| 12 × 12 ft | 1.78 | 2.67 | 1.96 |
| 20 × 12 ft | 2.96 | 4.44 | 3.26 |
| 20 × 20 ft | 4.94 | 7.41 | 5.43 |
| 24 × 24 ft | 7.11 | 10.67 | 7.82 |
| 30 × 30 ft | 11.11 | 16.67 | 12.22 |
Cubic yards = length × width (ft) × depth (in) ÷ 12 ÷ 27. Order on the +10 % figure for a slab on grade; round up to the increment your supplier sells.
| 1 | — |
|---|---|
| 2 | — |
| 3 | — |
| Cubic feet | — |
| Cubic yards | — |
| Cubic metres | — |
Twenty-seven cubic feet to the yard, and the depth is in inches. Slabs are 4 inches, footings 12, mulch 3; nobody measures those in feet, so the depth field takes inches and divides by twelve before it multiplies. A 20 × 12 slab at 4 inches is 80 cubic feet, 2.96 yards. Forgetting the twelve gives 960 cubic feet and a very surprised concrete plant.
Volume, not material. This is the geometry only. Concrete wants a waste factor, gravel a compaction allowance, excavated soil a swell factor, and each of those has its own page here that starts from this volume. Use this page when the question is simply how big the hole, the slab or the pile is.
Cylinders are footings and sonotubes. A 3-foot diameter pier 4 feet deep is 28.3 cubic feet, about a yard; twelve of them are twelve yards, which is a truck. The diameter is in feet here because piers are specified that way; a 12-inch sonotube is 1 foot.
What I check on a job
The inputs I check before I trust it. The arithmetic here is never what goes wrong; the inputs are. I take length and width from the dimensioned drawings, but I want the depth from the ground. On a 4-inch slab, whatever the subgrade is cut low is added to the thickness of the whole pour, so a small miss in the dirt becomes a real miss in the order. I ask for depths at several points and enter their average, not the number on the section. If one area is thicker than the field, such as a deeper strip under a wall, it goes in the second row with its own depth; anything beyond that I run separately and add. A single depth fudged to cover everything is worse than separate honest entries. Piers go in as dug, not as drawn, since the hole is what gets filled. Then I check the quantity fields last, because twelve piers entered as one is the easiest way for this page to be right and the order to be wrong.
Rectangular volume = length × width × depth ÷ 12; cylinder = π (d ÷ 2)² × depth. 1 yd³ = 27 ft³; 1 ft³ = 0.028316846592 m³ (exact).
Worked example
A 20 × 12 ft slab at 4 inches plus a 3 ft pier 4 ft deep: how many cubic yards?
- Slab: 20 × 12 × 4 ÷ 12 = 80 ft³.
- Pier: π × 1.5² × 4 = 28.27 ft³.
- 108.27 ft³ ÷ 27 = 4.01 yd³ (3.07 m³).
About 4 cubic yards of geometry — the concrete page adds the waste allowance on top of this figure.
5 values on this page were driven in a browser and compared with independently derived figures on 2026-10-29 (2808 values across 228 calculators site-wide).
Questions
How many cubic feet in a cubic yard?
27. A 20 × 12 ft slab 4 inches thick is 80 ft³, so 2.96 yd³.
How do you calculate cubic yards from inches?
Length × width in feet × depth in inches ÷ 12 gives cubic feet; divide by 27 for yards. The page takes depth in inches so the ÷ 12 cannot be forgotten.
How many yards is a 20 × 12 ft slab 4 inches thick?
80 cubic feet, 2.96 cubic yards. The depth goes in inches and is divided by twelve; forgetting that gives 960 cubic feet. That is the geometry only; concrete then wants a waste allowance, which the concrete page adds.
How much is a 3 ft pier 4 ft deep?
28.3 cubic feet, about one yard: π × 1.5² × 4. Twelve of them are about twelve yards, which is a truck. The diameter goes in feet; a 12 in. sonotube is 1 ft.