Slabs for a 12 × 10 ft shed base, by slab size
A 12 × 10 ft shed is a big workshop, a summerhouse or a small garden office. The base here is 3.6 × 3.0 m, converted at 0.3 m per foot, which leaves it marginally smaller than the shed floor as most shed makers ask (check your shed's instructions). The layout column shows where whole slabs fit with tight joints; the last column is the paving calculator's count with 10 mm joints and 10% for cuts and breakage.
| Slab size | Layout | Slabs by area | Slabs to buy |
|---|---|---|---|
| 600 × 600 mm | 6 × 5, no cuts | 30 | 32 |
| 450 × 450 mm | Needs cuts | 54 | 57 |
| 400 × 400 mm | Needs cuts | 68 | 71 |
| 300 × 300 mm | 12 × 10, no cuts | 120 | 124 |
| 600 × 300 mm | 6 × 10, no cuts | 60 | 63 |
| 900 × 600 mm | 4 × 5, no cuts | 20 | 22 |
Thirty slabs under a summerhouse or garden office
Six by five, 30 slabs, or 32 as the calculator counts them. A building this size is usually heavier than a garden shed and is often insulated and lined, so a rocking slab is harder to put right later. A full mortar bed suits it better than sand: 0.81 tonnes of sharp sand and 5 bags of cement.
The sub-base is 2.49 tonnes at 100 mm or 3.74 tonnes at 150 mm. Check the maker's instructions first: some garden rooms specify their own base, and a concrete slab here would be 1.19 m³.
Sub-base and bed for 3.6 × 3.0 m
| Layer | Quantity |
|---|---|
| MOT Type 1 sub-base, 100 mm | 2.49 tonnes |
| MOT Type 1 sub-base, 150 mm (soft ground) | 3.74 tonnes |
| Sharp sand for a 30 mm sand bed | 0.54 tonnes |
| Or a 40 mm mortar bed at 6:1 | 0.81 tonnes of sharp sand and 5 bags of 25 kg cement |
Quantities include 5% extra. Check for buried services before you dig, using the free LSBUD service. Shed base options compared weighs slabs against concrete, a plastic grid and a timber frame, and the concrete version of this base is on how much concrete for a 12 × 10 ft shed base.
Want to change anything else? The calculator above is the full Paving Slab Calculator (UK): edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
How many slabs do I need for a 12x10 shed base?
30 slabs of 600 × 600 mm, laid 6 by 5, cover the 3.6 × 3.0 m base with tight joints and no cuts. Buy 32 to have 2 spares; that is the paving calculator's count with 10 mm joints and 10% extra.
What goes under the slabs for a 12x10 shed base?
About 100 mm of compacted MOT Type 1 (2.49 tonnes for this base) and a 30 mm bed of sharp sand (0.54 tonnes). On soft ground use 150 mm of sub-base, which is 3.74 tonnes.
Can a summerhouse or garden office sit on paving slabs?
Many can, on a well compacted sub-base, but check the maker's instructions because some specify the base. For 3.6 × 3.0 m it is 30 slabs of 600 × 600 mm, ideally on a full mortar bed (0.81 tonnes of sand, 5 bags of cement).
Related sizes and guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check the Building Regulations and your supplier's guidance before ordering.