Concrete Calculator - How Much Concrete for a Slab (UK)
Work out how much concrete you need for a slab, base or footing - enter the dimensions and get the volume in cubic metres, ready for ready-mix or bagged.
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How to use this calculator
Enter the length, width and depth of your slab or base. Depth is in millimetres - 100mm is typical for a shed base or path, more for a driveway or load-bearing slab.
How we calculate this
- Volume = length × width × depth, plus 5% wastage (uneven sub-base, spillage).
- Above roughly 1.5 m³, ready-mix delivered is usually cheaper and easier than mixing on site.
- Bagged estimate assumes a 20kg pre-mix bag yields about 0.0095 m³.
Worked example
A 4m × 3m shed base at 100mm is 1.2 m³, plus 5% ≈ 1.26 m³ - round up to 1.3 m³ of ready-mix. That's a job for delivered concrete rather than dozens of bags by hand.
UK notes & gotchas
- Typical depths: 100mm for sheds/paths, 150mm+ for driveways, more again where vehicles or loads are involved.
- Use a C20-C25 mix for most domestic slabs; ask your supplier if you're unsure.
- A proper compacted sub-base and DPM under the slab matter as much as the concrete itself.
FAQ
How do I work out concrete volume?
Multiply length × width × depth (all in metres) for cubic metres, then add ~5% for wastage. This calculator does it for you, depth in mm.
Should I use ready-mix or bagged concrete?
Bagged is fine for small jobs (under ~1 m³). Above that, ready-mix delivered is usually cheaper, faster and more consistent.
How deep should a concrete slab be?
Around 100mm for a shed base or path; 150mm or more for driveways and anything load-bearing. Get advice for structural work.
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