Shed Base Concrete Slab Calculator
A 4 in slab on 4 in of compacted gravel is the standard base for a wood or metal shed. If the shed is big, sits on soft soil or holds a riding mower, add a thickened perimeter (a monolithic "turned-down" edge). This calculator handles both.
Common shed slab sizes (4 in slab, 10% extra)
| Shed | Flat slab | With 12 in wide × 8 in deep edge | Gravel base (4 in) | Form boards |
|---|---|---|---|---|
| 8 × 10 | 1.09 yd³ / 49 bags | 1.52 yd³ / 69 bags | 1.7 t | 36 ft |
| 10 × 12 | 1.63 yd³ / 74 bags | 2.17 yd³ / 98 bags | 2.56 t | 44 ft |
| 12 × 16 | 2.61 yd³ / 118 bags | 3.31 yd³ / 150 bags | 4.09 t | 56 ft |
How it's calculated
Slab volume = L × W × thickness ÷ 12. The thickened edge adds a 12 in wide band around the perimeter, as deep as the edge depth minus the slab thickness. Gravel base uses crusher run at about 1.5 tons per cubic yard, plus 15% for compaction. Rebar is laid out on an 18 in grid each way, plus 10% for laps.
Above about 1 cubic yard (a 10×12 slab is 1.5 yd³) a ready-mix truck often costs less and saves you from mixing 70+ bags. Run your numbers in the break-even calculator. If you'd rather set the shed on gravel, use the patio base calculator.
Frequently asked questions
How much concrete for a 10x12 shed slab?
At 4 in thick, a 10×12 slab is 40 cu ft (1.48 yd³). With 10% extra that's about 1.63 yd³, or 74 × 80 lb bags. A thickened edge adds about 0.4 yd³.
How thick should a shed slab be?
4 in is standard for sheds. Use 5–6 in or a thickened edge for heavy sheds, garages or riding-mower storage. Check local codes, since some require footings below the frost line.
Do I need rebar in a shed slab?
It isn't always required, but rebar or wire mesh helps keep cracks from spreading. It's cheap insurance.
Last reviewed October 2026 by Jim Frith. These are planning estimates; confirm quantities with your supplier and follow local codes.