Concrete slab volume by size
This table converts common rectangular slab dimensions into cubic feet and cubic yards. Use the calculator for different thicknesses or bag yields.
Published and reviewed: August 30, 2026 · Method: BetterHomeHabits calculator model
Concrete volume is length × width × thickness. Convert inches of thickness to feet, then divide cubic feet by 27 to get cubic yards. A purchase allowance can be added for spillage and site variation.
Reference table
| Slab size | Thickness | Volume incl. 10% | Cubic yards |
|---|---|---|---|
| 8 × 10 ft | 4 in | 29.3 cu ft | 1.09 yd³ |
| 10 × 10 ft | 4 in | 36.7 cu ft | 1.36 yd³ |
| 12 × 12 ft | 4 in | 52.8 cu ft | 1.96 yd³ |
| 15 × 15 ft | 4 in | 82.5 cu ft | 3.06 yd³ |
| 20 × 20 ft | 4 in | 146.7 cu ft | 5.43 yd³ |
Assumptions used
- 4 in slab thickness
- 10% planning allowance
- Rectangular slab
- No footings, thickened edges or grade beams
Why your result may differ
Real projects can differ because of product coverage, layout, waste, openings, moisture, compaction, site condition, labor scope or measurement error. Treat the table as a benchmark and use the linked calculator with the specifications for your actual project.
Methodology
The table is generated from the same transparent calculation method used by BetterHomeHabits calculators. We publish the assumptions so the numbers can be reproduced and challenged.