How Many Yards of Concrete Do I Need?
A 4-inch slab takes about 1.23 cubic yards per 100 square feet. Divide your square footage by 81 for a 4-inch pour, by 65 at 5 inches, or by 54 at 6 inches.
A 20 × 20 patio at 4 inches needs 4.94 yards, so you would order 5.5 yards after waste.
| Area | 4 in | 5 in | 6 in | 8 in |
|---|---|---|---|---|
| 100 sq ft | 1.23 yd³ | 1.54 yd³ | 1.85 yd³ | 2.47 yd³ |
| 200 sq ft | 2.47 yd³ | 3.09 yd³ | 3.70 yd³ | 4.94 yd³ |
| 300 sq ft | 3.70 yd³ | 4.63 yd³ | 5.56 yd³ | 7.41 yd³ |
| 400 sq ft | 4.94 yd³ | 6.17 yd³ | 7.41 yd³ | 9.88 yd³ |
| 600 sq ft | 7.41 yd³ | 9.26 yd³ | 11.11 yd³ | 14.81 yd³ |
| 800 sq ft | 9.88 yd³ | 12.35 yd³ | 14.81 yd³ | 19.75 yd³ |
| 1,000 sq ft | 12.35 yd³ | 15.43 yd³ | 18.52 yd³ | 24.69 yd³ |
Exact volume with no waste. Add 5–10% and round up to the next quarter yard.
How to work it out for your pour
Square footage divided by the coverage of one cubic yard at your thickness gives the answer directly. One cubic yard covers 81 sq ft at 4 inches, 65 sq ft at 5 inches, and 54 sq ft at 6 inches.
If you would rather work from raw dimensions: (length ft × width ft × thickness in ÷ 12) ÷ 27. The full method is on how to calculate yards of concrete.
Typical projects and what they take
- Shed pad, 10 × 10 at 4 in: 1.23 yd³
- Patio, 12 × 16 at 4 in: 2.37 yd³
- Single-car driveway, 10 × 20 at 5 in: 3.09 yd³
- Two-car garage floor, 24 × 24 at 4 in: 7.11 yd³
- Two-car driveway, 20 × 24 at 6 in: 8.89 yd³
- Shop floor, 30 × 40 at 6 in: 22.22 yd³ — two or three truckloads
How much waste to add
Nobody pours the exact calculated volume. Subgrade dips, forms bow slightly, and some concrete stays in the chute.
- 5% on a well-prepared, screeded base with tight forms
- 10% on rough ground, hand-dug footings, or anything you cannot re-measure
Running out mid-pour is far worse than over-ordering: the cold joint where the second load meets the first is a permanent weak point.
When you need more than one truck
A standard mixer carries 8–11 cubic yards but most deliver 9–10 because of road weight limits. Anything above about 10 yards means scheduling back-to-back loads so the pour stays continuous. See how many yards of concrete are in a truck before you book.
Estimating notes
- Orders under 3–5 yards usually trigger a short-load fee of $40–$60 per yard or $100–$180 flat.
- Measure the actual formed area, not the plan drawing — sites move.
- For irregular shapes, split the area into rectangles and circles and add the volumes.