How this calculator works
The pad is the shed plus an extension on each side. A gravel pad is the area times the compacted depth, converted to tons with 15% extra for compaction; a concrete slab is the area times the thickness over a 4 inch gravel base. A border of timbers or forms follows the perimeter.
Worked example: a 12 × 10 ft shed with the pad extended 12 inches each side is 14 × 12 ft (168 ft²). A 6 inch gravel pad takes 5.0 tons of crushed stone and 7 border timbers of 8 ft. A 4 inch concrete slab on the same area takes 2.28 cubic yards (103 bags of 80 lb) on 3.5 tons of gravel.
Gravel pad by shed size (6 in deep, 12 in extension)
Crushed stone with 15% extra.
| Shed | Pad | Stone | Border pieces (8 ft) |
|---|---|---|---|
| 8 × 8 ft | 100 ft² | 3.0 tons | 5 |
| 8 × 10 ft | 120 ft² | 3.6 tons | 6 |
| 10 × 12 ft | 168 ft² | 5.0 tons | 7 |
| 12 × 16 ft | 252 ft² | 7.5 tons | 8 |
| 12 × 20 ft | 308 ft² | 9.2 tons | 9 |
Tips before you buy
- Strip the grass and topsoil, and level the ground before you spread the stone. A pad that sits on topsoil will settle.
- Compact the stone in layers with a plate compactor, and check the level in several directions.
- Slope the ground around the pad so water runs away from it.
- A concrete slab is permanent and stronger, a gravel pad drains well and costs less. Choose by the weight of what you will store.
- Check the shed maker's warranty: many require a specific base.
Tools & materials for this project
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Frequently asked questions
How much gravel do I need for a 10x12 shed base?
About 5.0 tons of crushed stone for a 6 inch deep pad a foot larger than the shed on each side (168 ft²).
How thick should a gravel shed base be?
4 to 6 inches of compacted crushed stone is typical for a garden shed, over landscape fabric, with a timber border. Go deeper on soft ground.
How much concrete for a shed slab?
A 4 inch slab on a 168 ft² pad takes 2.28 cubic yards, or 103 bags of 80 lb, with 10% extra.
Gravel or concrete for a shed?
Gravel drains well, costs less and is easier to do yourself. Concrete is permanent, stronger and flatter. Follow the shed maker's requirement for the base.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.