Concrete needed for an 8 × 6 m slab, by thickness
These figures are for the whole 48 m² slab. The ready-mix column adds 10% for waste and rounds up to the next quarter m³, which is how most suppliers sell it. The cement bags are for mixing it yourself at 1:2:4.
| Thickness | m³ (no waste) | m³ with 10% waste | Ready-mix to order (m³) | Weight (tonnes) | Bags of cement (25 kg) |
|---|---|---|---|---|---|
| 75 mm | 3.60 | 3.96 | 4.00 | 9.5 | 51 |
| 100 mm | 4.80 | 5.28 | 5.50 | 12.7 | 67 |
| 125 mm | 6.00 | 6.60 | 6.75 | 15.8 | 84 |
| 150 mm | 7.20 | 7.92 | 8.00 | 19.0 | 101 |
What an 8 × 6 m slab is used for
An 8 × 6 m slab is a large garage, barn or workshop floor. This is a structural job: follow the engineer or building control specification for thickness, mesh and a damp-proof membrane.
Bags or ready-mix for 8 × 6 m?
At 5.28 m³ ready-mix is the sensible choice. Mixing by hand would be 67 bags of cement and over 10.7 tonnes of sand and aggregate to mix and place before the first batch sets. Order 5.50 m³, and have the shuttering and helpers ready before the lorry arrives.
Don't forget the sub-base and the reinforcement
A slab needs a compacted sub-base, usually 100 mm of MOT Type 1, which for 48 m² is about 11.1 tonnes with 5% for compaction (see the gravel calculator). Vehicles need mesh such as A142 and movement joints. For a patio on top of the slab, the paving calculator gives the slabs and sand. Check for buried services before you dig.
Want to change anything else? The calculator above is the full Concrete Calculator (UK, m³): edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
How much concrete do I need for an 8m x 6m slab?
An 8 × 6 m slab is 48 m². At 100 mm thick that is 4.80 m³, or 5.28 m³ with 10% extra, so order 5.50 m³ of ready-mix. At 150 mm it is 7.20 m³, or 7.92 m³ with 10% extra.
How many bags of cement for an 8m x 6m slab?
For a 1:2:4 mix at 100 mm with 10% extra you need about 67 bags of 25 kg cement, 3.72 tonnes of sharp sand and 6.97 tonnes of 20 mm aggregate. At 150 mm it is 101 bags.
How much does an 8m x 6m concrete slab weigh?
At 100 mm thick it weighs about 11.5 tonnes, using 2.4 tonnes per m³. At 150 mm it is about 17.3 tonnes.
Related sizes and guides
Related sizes
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.