A three-step slab estimator
- Area. Length × width in feet. A 24 × 30 garage is 720 square feet.
- Concrete. Area × thickness in feet ÷ 27 = cubic yards. At 4 inches (0.333 ft): 720 × 0.333 ÷ 27 ≈ 8.9 yards, before thickened edges and about 5–10% waste.
- Installed range. Area × a national per-square-foot range. At $4–$8: about $2,880–$5,760 for that 720 square feet.
Common sizes
| Slab | Sq ft | Yards at 4 in | Yards at 6 in | At $4–$8 per sq ft |
|---|---|---|---|---|
| 10 × 12 shed pad | 120 | 1.5 | 2.2 | $480–$960 |
| 12 × 40 RV pad | 480 | 5.9 | 8.9 | $1,920–$3,840 |
| 24 × 24 garage | 576 | 7.1 | 10.7 | $2,304–$4,608 |
| 30 × 40 shop | 1,200 | 14.8 | 22.2 | $4,800–$9,600 |
| 40 × 60 shop | 2,400 | 29.6 | 44.4 | $9,600–$19,200 |
Yards cover the flat area only. Dollar figures use the national $4–$8 range for most slabs; reinforced slabs run above $10 per square foot in national guides, and small pads often carry a minimum charge. None of these are quotes.
Why building slabs cost more
A shop or garage floor is not just a big patio. Thickened edges or grade beams carry the walls, and they take extra concrete and digging, which is slower where caliche sits close to the surface. Anchor bolts have to be set to the building supplier's drawings. Plumbing and conduit go in first. A vapor barrier goes under heated space. Each item adds labor that a flat pad does not need. See concrete slabs and shop pads and footings and foundations.
Costs that are easy to miss
- Pad prep: fill to raise the slab above surrounding grade, compacted in lifts.
- Removal of an old slab or caliche spoil haul-off.
- Pump truck where a mixer cannot reach the forms.
- A culvert permit and culvert if a new drive crosses a county road ditch (the county permit itself is free).
- Winter blankets or summer curing compound.
- Saw-cutting joints the day after the pour.
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