Shed Foundation Materials List: Gravel Pad or Concrete Slab
Part of the project planner: Planning a shed, pergola, garage slab or coop.
A shed 12 × 10 ft needs a foundation about a foot larger all round. A gravel pad takes 5.0 tons of crushed stone, 7 timbers for the border and 185 ft² of fabric. A concrete slab takes 2.28 cubic yards (103 bags of 80 lb), 3.5 tons of base stone and 4 sheets of mesh.
The materials list
Gravel pad
| What to buy | How much | How we worked it out |
|---|---|---|
| Crushed stone | 5.0 tons | Shed foundation calculator: 168 ft² (the shed plus 12 in all round), 6 in compacted, plus 15% for compaction |
| Timber border | 7 pieces of 8 ft | 4×4 or 4×6 treated timber around the edge, staked at the corners |
| Landscape fabric | 185 ft² | Under the gravel, with overlaps, to stop weeds and mixing with the soil |
| Skids or blocks | As the shed maker says | Solid blocks on the gravel keep the shed floor off the ground |
Concrete slab
| What to buy | How much | How we worked it out |
|---|---|---|
| Concrete | 2.28 yd³ (103 bags of 80 lb) | Same calculator, slab: 4 in thick, 10% extra |
| Crushed stone base | 3.5 tons | A 4 in compacted base under the slab |
| Form boards | 7 boards of 8 ft (2×6) | Around the edge, staked |
| Wire mesh | 4 sheets of 5 × 10 ft | Held mid-depth on chairs |
Materials for other shed sizes
Pad 12 inches larger on every side. Gravel pad 6 inches deep; slab 4 inches thick:
| Shed | Gravel pad stone | Border timbers | Slab concrete | Slab 80 lb bags |
|---|---|---|---|---|
| 8 × 6 ft | 2.4 tons | 5 | 1.1 yd³ | 49 |
| 10 × 8 ft | 3.6 tons | 6 | 1.6 yd³ | 74 |
| 10 × 12 ft | 5.0 tons | 7 | 2.3 yd³ | 103 |
| 12 × 16 ft | 7.5 tons | 8 | 3.4 yd³ | 154 |
| 12 × 20 ft | 9.2 tons | 9 | 4.2 yd³ | 189 |
| 16 × 20 ft | 11.8 tons | 10 | 5.4 yd³ | 242 |
Gravel or concrete?
| Gravel pad | Concrete slab | |
|---|---|---|
| Cost | Lower | Higher |
| Effort | Moderate: dig, compact, fill | More: forms, steel, pour, finish |
| Drainage | Excellent | Needs a slight slope |
| Best for | Light sheds up to about 10 × 12 ft | Large sheds, workshops, heavy equipment |
| Permit | Often not needed | Often needed |
Before you build
- Choose a level, well-drained spot away from trees and the property line, and check your local setback rules.
- Call 811 before you dig.
- Dig out the topsoil, compact the subgrade and add the base in layers of 4 inches or less, compacting each.
- Check the pad is level in both directions with a long straight board and a level, and square by measuring the diagonals with the check square calculator.
- Check the shed maker's foundation instructions, since some warranties require one.
See also the garage slab materials list and the gravel driveway materials list. Estimates only: check your local code, and follow the product labels.
Frequently asked questions
How much gravel do I need for a 12x10 shed base?
5.0 tons of crushed stone for a pad 12 inches larger on each side, 6 inches deep, with 15% extra: 168 ft² in all.
How much concrete for a 12x10 shed slab?
2.28 cubic yards (103 bags of 80 lb) for a pad 168 ft² and 4 inches thick, with 10% extra. At 6 inches it is 3.42 cubic yards.
Is a gravel pad or a concrete slab better for a shed?
A gravel pad is cheaper, drains well and is easy to build; a concrete slab is stronger and flatter, and it suits heavier sheds and workshops. Both need a level, compacted base.
How big should the foundation be?
About 6 to 12 inches larger than the shed on every side, so that the shed sits fully on the base and the rain running off the roof soaks away at the edge of the stone.
Do I need a permit for a shed foundation?
Often not for a small shed on a gravel pad, but many places require a permit above a certain size (commonly 100 to 200 square feet), and a slab usually needs one. Check with your building department.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.