Concrete Calculator — How Much Concrete Do I Need?
Pick a shape, put in your measurements and get the exact cubic metres — plus what to actually order and the mix we'd batch for the job. No email address demanded, no nonsense.
Updated: July 2026
Work Out Your Volume
Lengths and widths in metres, depths in millimetres — we do the conversion. Results in cubic metres (m³).
Please enter measurements above zero for every field in your chosen shape.
Exact volume: 0.00 m³
- Order with 5% contingency: 0.00 m³
- Order with 10% contingency: 0.00 m³
Recommended mix:
Order volumes are rounded up to the nearest 0.25m³ (0.5m³ minimum). And because we batch on site and meter the discharge, you only pay for what's actually poured — contingency that stays in the truck costs you nothing.
How to Measure Up
- Slabs: longest side × widest side, in metres. An L-shaped slab is just two rectangles — work them out separately and add the volumes together.
- Trenches: add up the running length of every trench, then use the width and depth as dug — not as drawn. Trenches rarely come out exactly to plan.
- Circular pads: measure the diameter straight across the middle. The calculator does π × (diameter ÷ 2)² × depth for you.
- Depths are in millimetres: 100mm = 0.1m, 150mm = 0.15m, 1m = 1000mm. Getting the units wrong is the classic ten-times-too-much mistake — the calculator converts for you.
- Why the contingency? Sub-bases are never perfectly flat and trenches never perfectly straight. 5–10% extra covers the low spots and the spillage.
Measuring for a specific job? See our pages on concrete for foundations, concrete for driveways and concrete for shed and garage bases for depths, mixes and worked examples.
Worked Examples
A garage-sized slab. 6m long × 3m wide at 150mm deep: 6 × 3 × 0.15 = 2.7m³. Add 5–10% contingency and you'd order 3m³.
Extension footings. 12m of trench, 600mm wide, dug to 1m deep: 12 × 0.6 × 1.0 = 7.2m³. With contingency, order 7.75–8m³.
A circular pad — say for a garden building — 3m across at 100mm deep: π × 1.5² × 0.1 = 0.71m³. Order 0.75m³. Yes, we deliver loads that small — our minimum is 0.5m³ with no part-load penalty.
If your numbers look wildly different from these, check the depth units first. It's nearly always the depth units.
Getting the Order Right
The maths is simple: volume = length × width × depth, all in metres (100mm = 0.1m). Then add 5–10% contingency, because real ground is never as tidy as the drawing.
With a drum supplier you're threading a needle: don't wildly over-order, because you pay for every cubic metre on the truck plus disposal of what comes back — but under-order and you're waiting on a second delivery. With volumetric supply the needle disappears: we carry more material than the job needs, batch on site, and the meter records what's discharged. You only pay for what's poured.
A few numbers worth knowing before the truck arrives:
- 1m³ of concrete weighs about 2.4 tonnes. If the chute can't reach the pour, that's roughly 20 barrow loads per cubic metre — plan your labour, or ask us about pumping.
- Slab depth guidance: paths and shed bases around 100mm; driveways and garage floors around 150mm.
- Foundation depths aren't a rule of thumb — they're set by your engineer or building control from the ground conditions. Measure the trench as dug.
What Your Volume Costs
Multiply your cubic metres by the grade price and you've got a working budget. Our guide prices — all per m³, +VAT, confirmed when you book:
| Mix | Typical use | Guide price per m³ |
|---|---|---|
| C8/10 (GEN1-equivalent) | Strip & trench-fill foundations, oversite, floors to be screeded | from £99 |
| C20 (C16/20, GEN3-equivalent) | Unreinforced shed, garage & workshop bases | from £105 |
| C25 (C25/30) | Reinforced foundations & general structural | from £110 |
| C30 | External durability; air-entrained PAV1-equivalent for driveways | from £115 |
| C35 (C28/35) | Reinforced garage floors, structural & suspended work | from £120 |
| C40 (C32/40) | Heavy-duty salted paving (PAV2-equivalent), industrial wearing surfaces | from £128 |
So the 2.7m³ garage slab above, poured in C20 at £105: roughly £284 +VAT of concrete, metered as it's poured. For the full breakdown — grades, pumping, small loads, surcharges — see our ready mix concrete prices guide, or read concrete grades explained if you're not sure which mix your job needs.
Concrete Calculator FAQs
How much is a cubic metre of concrete?
As a guide, from £99 per m³ +VAT for a C8/10 (GEN1-equivalent) foundation mix up to £128 per m³ +VAT for C40. Most domestic jobs land between £105 and £120 per m³ +VAT. Guide prices, confirmed when you book — full detail in our concrete prices guide. Every m³ is metered, so you only pay for what's poured.
How do I work out how much concrete I need?
Length × width × depth, all in metres. Convert the depth first: 150mm is 0.15m. A 6m × 3m slab at 150mm is 6 × 3 × 0.15 = 2.7m³. Add 5–10% contingency and round up to the nearest quarter cube — or let the calculator above do all of it.
How much does a cubic metre of concrete weigh?
Roughly 2.4 tonnes. That's why concrete arrives on a big truck — and why barrowing more than a couple of cubic metres is serious graft: reckon on about 20 barrow loads per m³ at over 100kg a barrow.
What happens if I order too much or too little concrete?
With drum-mixed concrete both mistakes cost money: over-order and you've paid for concrete you don't use, plus disposal of the surplus; under-order and you're waiting on a second delivery with part-load fees. Volumetric supply fixes this — we carry more material than the job needs, batch on site and meter what's discharged. You pay for what's poured and nothing else.
How thick should my concrete slab be?
Rule of thumb: paths and shed bases around 100mm; driveways and garage floors around 150mm. Foundations are different — trench depth is set by your engineer or building control from the ground conditions, not by a rule of thumb.
Know Your Volume? Get Your Price.
Call with the number — or send us the dimensions and we'll double-check the maths before we quote. Batched on site, metered as it pours, from 0.5m³.