Estimate materials, thickness, sub-base, labour, and cost — for garages, garden rooms, driveways, and more.
How Concrete Volume Is Calculated
Concrete volume is calculated by multiplying the total floor area by the required thickness of the slab. This gives you the volume in cubic metres (m³), which is the standard unit for ordering ready-mix or batching your own mix.
Formula:
Length × Width × Depth = Volume (m³)
- Length: Total length of the slab in metres
- Width: Total width in metres
- Depth: Thickness of the slab in metres (e.g. 100mm = 0.1m)
Example:
A garage floor that’s 6 metres long, 4 metres wide, and 0.1 metres thick would be:
6 × 4 × 0.1 = 2.4m³
You would need at least 2.4 cubic metres of concrete for this job — plus a little extra for waste and levelling.
Don’t Forget to Add 5–10% for Waste
Concrete isn’t poured perfectly flat every time, and some volume is lost during handling. It’s standard practice to add 5–10% extra to your total to cover spillage, uneven ground, or topping up at the edges.
🔹
How do I calculate how much concrete I need for a floor?
To calculate how much concrete you need, multiply the floor area (length × width) by the thickness of the slab in metres. This gives you the volume in cubic metres (m³). For example, a 5m × 4m slab at 0.1m thick = 2.0m³. It’s smart to add 5–10% extra for waste and uneven surfaces.
🔹
What is the standard thickness for a concrete floor?
For domestic use like garages, sheds, and garden rooms, the typical concrete slab thickness is 100mm (0.1m). Heavier-duty slabs for driveways or commercial use often go up to 125mm or 150mm. Always match the depth to the load and sub-base quality.
🔹
How much does concrete cost per m² in the UK?
The average cost of concrete in the UK is £120–£150 per cubic metre (m³), including delivery. To convert that into a cost per m², multiply by your slab thickness (e.g. 0.1m for 100mm). That gives you roughly £12–£15 per m², plus labour and extras like mesh or DPM.
🔹
Should I include a sub-base in my calculation?
Yes — the sub-base is essential for strength and drainage. MOT Type 1 or lean mix concrete is usually laid to a depth of 100–150mm beneath the slab. This adds cost and depth to your project, but skipping it can lead to slab cracking or sinking over time.
🔹
Is underfloor heating included in concrete floor depth?
Yes. When using underfloor heating, the pipes are usually set into insulation with a flowing screed poured over them. The concrete calculator will add a screed layer and adjust the depth accordingly. It’s typically a separate 40–50mm layer above the heating pipes.
Home
Calculators
Services
Locations
Blog
Contact 