Calculator
Shed Foundation Calculator
For an 8x10 shed with a 1 ft border, a 4 in gravel pad takes about 1.6 cubic yards (roughly 2.3 tons with compaction), a 4 in concrete slab takes about 1.1 cubic yards (49 bags of 80 lb mix), and a 16 in paver base takes 48 pavers. Gravel is usually the cheapest and drains best under resin and metal kits.
Shed foundation calculatorUpdates as you type
Gravel pad: 2.3 tons, about $103
- Gravel pad size
- 10 x 12 ft
- Gravel (4 in, compacted)
- 1.63 yd³ / 2.3 tons
- Concrete slab (4 in)
- 1.09 yd³ / 49 bags of 80 lb
- Concrete material cost
- $319
- 16 in pavers
- 48 pavers
- Paver base (4 in gravel + 1 in sand)
- 1.5 t gravel + 0.3 t sand
- Paver material cost
- $275
- Weed fabric for the pad
- 120 sq ft
Material costs only; add delivery and rental of a plate compactor.
Foundation kits and site prep tools
Matched to this result, spread from budget to premium.
Prices change often; the button shows today's price on Amazon.
Which shed foundation is best?
For resin and steel kits under about 150 sq ft, a compacted gravel pad inside a treated timber frame is the best value: it drains, stays level, and costs a fraction of a slab. Concrete is the right call for heavy use (a garage-sized shed, a workshop, a riding mower driven in daily) or when the kit's floor is thin and needs a rigid base. Pavers sit between the two: neat and flat, but slower to level than gravel. Gravel vs concrete covers the tradeoffs in detail.
The assumptions behind each number
| Input | Default | Basis |
|---|---|---|
| Gravel border | 1 ft each side | Common kit instruction; catches roof drip |
| Gravel density | 1.4 t per cubic yard | Supplier conversion for 3/4 in crushed stone |
| Compaction allowance | +10% | Trade convention |
| 80 lb concrete bag yield | 0.6 cu ft | Printed on the bag |
| Concrete waste | +10% | Trade convention |
| Paver base | 4 in gravel + 1 in sand | Standard paver installation |
Prices are defaults you can change. Quarries typically deliver a minimum of several tons, so small pads may cost the delivery minimum rather than the per-ton price.
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Frequently asked questions
Can I put a shed directly on the ground?
Not for long. Bare soil holds moisture against the floor, settles unevenly and lets the doors rack out of alignment. Even a small resin shed does better on a few inches of compacted gravel or a plastic grid foundation kit, which keeps the floor dry and level for far longer than grass or dirt.
How thick should a shed slab be?
Four inches of concrete over a compacted gravel sub-base is standard for storage sheds. Go to 6 in, or thicken the edges, if you will drive a lawn tractor in regularly or build a large workshop. The calculator shows both so you can see the extra bags.
Is a plastic shed foundation kit as good as gravel?
For small and mid-size resin sheds on reasonably level ground, grid kits work well: they lock together, spread the load and drain. On a slope, or for a large or heavy shed, a proper compacted gravel pad inside a timber frame is more forgiving.
This page is researched guidance, not professional engineering, legal or building-code advice. Sizes, loads and permit rules vary by product and by town: check your local code and the kit manufacturer's instructions before you build.