Free UK construction calculators Metric and imperial 2026 UK prices
Work out how much concrete you need for a slab, a strip footing, pads, round columns or post holes, or a set of steps. Enter the sizes, press Calculate, and see the cubic metres, the ready-mix to order, the cement and ballast to mix it yourself, the 20 kg bags, and which way is cheapest.
Concrete Needed
0m³
Check the measurements above. The result updates once they look right.
| Method | What To Order | Cost |
|---|
Typical 2026 UK prices including VAT. Ready-mix includes a 1 m³ minimum and the part-load charge under 4 m³; pump hire is extra.
| Unit | Amount |
|---|
Including your extra. Concrete weighs about 2.4 tonnes per m³.
The result gives the volume in cubic metres, yards and feet, the weight, the ready-mix to order, the cement, ballast and water to mix it yourself, the number of 20 kg bags, and the cost of each so you can see the cheapest way to buy it.
Concrete is sold by the cubic metre (m³), so every job comes down to length × width × depth, with all three in metres. A slab 4 m long, 3 m wide and 100 mm thick is 4 × 3 × 0.1 = 1.2 m³.
| Shape | Formula | Example |
|---|---|---|
| Slab | Length × width × thickness | 4 m × 3 m × 0.1 m = 1.2 m³ |
| Strip footing | Trench length × width × depth | 10 m × 0.6 m × 0.225 m = 1.35 m³ |
| Square pad or column | Length × width × depth × number | 0.6 × 0.6 × 0.45 m × 4 = 0.65 m³ |
| Round column or hole | 3.1416 × radius² × depth × number | Ø 300 mm × 600 mm = 0.042 m³ each |
| Solid steps | Width × going × rise × n × (n + 1) ÷ 2 | 3 steps, 1.2 m × 300 mm × 150 mm = 0.32 m³ |
The most common mistake is mixing units: 100 mm is 0.1 m, not 1 m. The calculator takes slab sizes in metres and thicknesses in millimetres to avoid this, and warns you if a number looks like the wrong unit.
| Job | Concrete thickness | On |
|---|---|---|
| Garden path | 75–100 mm | 75–100 mm of Type 1 |
| Shed or greenhouse base | 75–100 mm | 75–100 mm of Type 1 |
| Patio | 100 mm | 100 mm of Type 1 |
| Car driveway | 100–150 mm | 150 mm of Type 1, with mesh or fibres |
| Garage floor | 100–150 mm | Type 1, sand blinding and a damp-proof membrane |
| Strip footing | At least 225 mm, usually more | Firm natural ground at the depth Building Control agrees |
| Fence post hole | About a third of the post height deep | A little gravel in the bottom for drainage |
For the details of each job, our concrete slab calculator, concrete footing calculator and concrete driveway calculator add the sub-base, reinforcement and joints.
| Slab size | At 100 mm | At 150 mm |
|---|---|---|
| 2 × 2 m | 0.40 m³ | 0.60 m³ |
| 3 × 3 m | 0.90 m³ | 1.35 m³ |
| 4 × 3 m | 1.20 m³ | 1.80 m³ |
| 6 × 3 m | 1.80 m³ | 2.70 m³ |
| 5 × 4 m | 2.00 m³ | 3.00 m³ |
| 10 × 5 m | 5.00 m³ | 7.50 m³ |
| Hole | Volume | Litres | 20 kg bags (with 10%) |
|---|---|---|---|
| Ø 250 × 600 mm | 0.030 m³ | 30 L | 4 |
| Ø 300 × 600 mm | 0.042 m³ | 42 L | 5 |
| Ø 300 × 750 mm | 0.053 m³ | 53 L | 7 |
| Ø 400 × 900 mm | 0.113 m³ | 113 L | 14 |
The slab table is the exact volume; order about 10% more. The hole table includes 10% extra in the bag count, at about 105 bags of dry mix per m³ of finished concrete.
| Method | Best for | Watch out for |
|---|---|---|
| 20 kg bags of ready-to-use concrete | Under about 0.25 m³: post holes, small repairs | About 105 bags per m³, so the cost climbs fast |
| Cement and ballast, mixed on site | About 0.25–1 m³ when you have a mixer and help | Hard work; batches vary if you do not measure carefully |
| Volumetric (mini-mix) lorry | 0.5–4 m³, paying only for what is used | A higher price per m³ than a full ready-mix load |
| Ready-mix (drum) lorry | Over about 3–4 m³ | Part-load charges under the minimum load, and only 30–60 minutes to unload |
Small orders are where people overspend. Most ready-mix plants run 6 m³ and 8 m³ lorries and set a minimum load of around 3–4 m³, adding a part-load charge of about £15–£30 for each cubic metre short. The calculator includes that charge, which you can change or set to 0 for a volumetric supplier. Our ready-mix concrete cost calculator and concrete bag calculator go into each option in more depth.
| Mix (cement : all-in ballast) | Use | Cement per m³ | Ballast per m³ |
|---|---|---|---|
| 1:4 | Driveways, columns, heavy bases | 360 kg (14.4 bags) | 1.70 t |
| 1:5 | Slabs, shed bases, paths, steps | 300 kg (12 bags) | 1.77 t |
| 1:6 | Footings, foundations, post holes | 257 kg (10.3 bags) | 1.82 t |
All-in ballast is sand and gravel already blended, so a 1:5 mix is one bucket of cement to five of ballast, which is close to the classic 1:2:4 of cement, sand and gravel. The dry materials add up to about 1.25 m³ for every cubic metre of concrete, because the sand fills the gaps between the stones. Add water a little at a time: too much makes weak, dusty concrete. See our concrete mix ratio calculator for C-grade equivalents.
| Item | Typical 2026 UK price |
|---|---|
| Ready-mix, general purpose, per m³ | £100–£160 |
| Part-load charge, per m³ short of the minimum | £15–£30 |
| Volumetric mini-mix, per m³ | £100–£160 |
| 20 kg bag of ready-to-use concrete | £4.50–£6.50 |
| Cement, 25 kg bag | £7–£8 |
| All-in ballast, bulk bag | £60–£80 |
| Concrete pump hire, per day | £280–£800 |
Ready-mix prices include VAT here, as the calculator's defaults do. Ask each supplier for the full price, including delivery, part-load, waiting time and any Saturday charge, before you compare. Fibre reinforcement or a stronger mix adds to the price per m³.
Foundations for extensions, garages and outbuildings that need approval come under Part A of the Building Regulations. The size and depth depend on the ground and the load, and Building Control inspects the trench before you pour. The government's Approved Document A sets out the guidance. This calculator works out quantities only: it does not design foundations, so get the sizes from your drawings, an engineer or Building Control.
Concrete (m³) = volume of the shape × (1 + extra %) · Weight = m³ × 2.4 tonnes
Mix on site: dry materials = m³ × 1.25 · Cement (kg) = dry ÷ (1 + n) × 1,440 · Ballast (t) = dry × n ÷ (1 + n) × 1.7
Ready-mix = m³ rounded up to the next 0.25 m³ · Bags = m³ × 2,100 kg ÷ 20 kg
Here n is the ballast in the mix, such as 5 for 1:5. Cement is rounded up to whole 25 kg bags and ballast to 850 kg bulk bags, or 20 kg bags below 0.3 tonnes. Ready-mix is charged at a minimum of 1 m³, with your part-load charge for each m³ under 4 m³. These are the same figures as our cement calculator and ballast calculator, so results match across the site.
Multiply length × width × depth, all in metres, to get cubic metres, then add about 10% for spills and uneven ground. A 4 × 3 m slab, 100 mm thick, is 1.2 m³, so order about 1.3 m³.
About 105 bags, because a 20 kg bag makes roughly 0.0095 m³ of finished concrete. That is why bags only make sense for small jobs.
For a general 1:5 mix, about 300 kg of cement (12 × 25 kg bags) and 1.77 tonnes of all-in ballast.
About 2.4 tonnes. A 20 kg bag of dry mix makes about 9.5 litres of concrete.
Under about 0.25 m³, bags are usually cheapest. Between about 0.25 and 3 m³, compare mixing on site with a volumetric supplier. Over about 3–4 m³, ready-mix is almost always cheaper and quicker.
Many plants charge for at least 1 m³ and add a part-load charge for each m³ under a minimum load of about 3–4 m³. Volumetric suppliers often deliver from 0.25–0.5 m³ with no part-load charge.
75–100 mm for paths and shed bases, 100 mm for patios, and 100–150 mm for driveways and garage floors, on a compacted sub-base.
About 30–50 litres for a typical 300 mm wide hole, 600–750 mm deep, which is four to seven 20 kg bags. The post itself takes up a little of that.
Cement at 1,440 kg/m³, all-in ballast at 1.7 t/m³, a dry volume factor of 1.25, bagged mix at 2,100 kg per m³ placed and concrete at 2.4 t/m³, as across ConstructionMath. Default prices are typical 2026 UK prices including VAT; part-load charges and minimum loads come from UK supplier and cost guides and vary by plant and region. Reviewed November 2026.