Free UK construction calculators Metric and imperial 2026 UK prices
Work out how many bags of cement you need for concrete, bricklaying mortar, floor screed or render. Choose the job, enter the size and the mix, and the calculator gives the 25 kg bags of cement, the sand or ballast, the water and the cost of materials.
Cement To Buy
0bags
Check the measurements above. The result updates once they look right.
| Mix | Bags | Sand Or Ballast | Use For |
|---|
For the same amount as your result. Your mix is highlighted.
| Item | Buy | Cost |
|---|
Uses the prices above. A bulk bag holds about 850 kg.
The result shows the 25 kg bags of cement to buy, the sand or ballast in tonnes and bags, roughly how much water to use and the cost. A table compares the cement for every mix, so you can see how much a stronger or weaker mix changes the order.
The table shows the cement in one cubic metre of finished mix, before any extra for waste.
| Mix | Used for | Cement per m³ | 25 kg bags | Sand or ballast |
|---|---|---|---|---|
| 1:4 cement to ballast | Strong concrete | 360 kg | 14.4 | 1.70 t ballast |
| 1:5 cement to ballast | General concrete | 300 kg | 12 | 1.77 t ballast |
| 1:6 cement to ballast | Footings, post holes | 257 kg | 10.3 | 1.82 t ballast |
| 1:8 cement to ballast | Blinding, kerb bedding | 200 kg | 8 | 1.89 t ballast |
| 3:1 sand to cement | Strong mortar, screed | 479 kg | 19.2 | 1.60 t sand |
| 4:1 sand to cement | Mortar, screed | 383 kg | 15.3 | 1.70 t sand |
| 5:1 sand to cement | Mortar, render | 319 kg | 12.8 | 1.77 t sand |
| 6:1 sand to cement | Soft mortar, render | 274 kg | 10.9 | 1.82 t sand |
Sand and cement mixes need more cement per m³ than concrete. In concrete, the stones in the ballast take up a lot of the space. In mortar and screed, fine sand has more surface for the cement to coat.
Most small UK jobs use all-in ballast, which is sand and gravel already mixed. A 1:5 mix of cement to ballast is a good general concrete for shed bases, paths and patios. It needs about 33 kg of cement for each m² of slab 100 mm thick, including 10% extra.
| Mix | Typical use | Roughly like |
|---|---|---|
| 1:4 | Driveways, garage floors, heavy bases | A strong 1:1.5:3 mix with separate sand and gravel |
| 1:5 | Shed bases, paths, patios, steps | A general 1:2:3 mix |
| 1:6 | Strip footings, foundations, fence and gate posts | A 1:2:4 mix |
| 1:8 | Blinding, kerb and edging haunching | A lean 1:3:6 mix |
A single 300 mm wide post hole 600 mm deep takes about 12 kg of cement at 1:6, or half a bag. If you need ballast on its own, or the full ballast order, our ballast calculator works it out, and the concrete slab calculator covers bigger slabs.
| Wall | Mortar per m² | Cement for 10 m² | Building sand |
|---|---|---|---|
| Half-brick wall (102.5 mm) | 23 litres | 4 bags (96 kg) | 429 kg |
| One-brick wall (215 mm) | 59 litres | 10 bags (248 kg) | 1.1 t |
| Cavity wall (brick and 100 mm block) | 33 litres | 6 bags (138 kg) | 613 kg |
| 100 mm blocks | 10 litres | 2 bags (42 kg) | 184 kg |
| 140 mm blocks | 14 litres | 3 bags (58 kg) | 258 kg |
| 215 mm blocks | 21 litres | 4 bags (89 kg) | 397 kg |
These include 10% extra. The mortar per m² matches our brick calculator and block calculator, which also count the bricks or blocks you need. Most walls above ground use a 4:1 or 5:1 mix with a plasticiser. Use a stronger 3:1 below ground and for copings, and a softer mix with soft or old bricks.
| Depth | Cement per m² | Sharp sand per m² | Bags for 10 m² |
|---|---|---|---|
| 40 mm (bonded) | 17 kg | 75 kg | 7 |
| 50 mm | 21 kg | 94 kg | 9 |
| 65 mm (over insulation) | 27 kg | 122 kg | 11 |
| 75 mm (over underfloor heating) | 32 kg | 140 kg | 13 |
These include 10% extra. A traditional floor screed is 1 part cement to 4 parts sharp sand, laid semi-dry and compacted. A cubic metre of laid screed weighs about 2.1 tonnes, so it uses more cement than people often expect. Screed laid over insulation or heating pipes should be at least 65 mm thick.
Sand and cement render is usually two coats, about 15–20 mm in total. At 5:1, a 20 mm render uses about 7 kg of cement and 39 kg of plastering sand per m². So 20 m² of wall needs about 6 bags of cement and 780 kg of sand.
The first coat, called the scratch coat, can be a little stronger, such as 4:1. The top coat should be the same or weaker, such as 5:1 or 6:1 with a part of hydrated lime. On old solid walls, a breathable lime render is usually a better choice than cement.
Loose sand, ballast and cement take up more room than the finished mix, because the fine particles fill the gaps when water is added. That is what the 1.25 and 1.33 factors allow for. Cement is taken at 1,440 kg per m³, building and sharp sand at 1.6 tonnes per m³ and all-in ballast at 1.7 tonnes per m³. Bags are always rounded up.
A base 3 m × 2 m × 100 mm deep is 0.6 m³. Adding 10% gives 0.66 m³. At 1:5 cement to ballast, that needs 198 kg of cement, so 8 bags, and about 1.17 tonnes of all-in ballast.
10 m² of half-brick wall uses about 0.25 m³ of mortar with 10% extra. At 4:1, that is 96 kg of cement, so 4 bags, and about 430 kg of building sand.
A 15 m² floor screeded 65 mm deep is 0.975 m³, or 1.07 m³ with 10% extra. At 4:1, it needs 411 kg of cement, so 17 bags, and 1.83 tonnes of sharp sand.
Wet cement is strongly alkaline. It can cause serious burns if it is trapped against the skin, for example inside a boot or glove, and it is a common cause of dermatitis. Wear waterproof gloves, long sleeves and eye protection, wash cement off your skin straight away, and do not kneel in wet concrete. The HSE guidance on cement explains the risks and how to control them. A 25 kg bag is also heavy, so lift it close to your body and get help where you can.
About 12 bags of 25 kg for a general 1:5 mix with all-in ballast, or about 10 bags for a 1:6 mix. Add 10% for waste.
About 15 bags of 25 kg at 4:1 sand to cement, or about 13 bags at 5:1. You also need around 1.7 tonnes of building sand.
1,000 bricks build about 16.9 m² of half-brick wall, which needs about 7 bags of cement at 4:1 and around 720 kg of building sand.
At 4:1, a bulk bag of about 850 kg of sand pairs with roughly 8 bags of cement. At 5:1, it is about 6 bags.
1 part cement to 5 parts all-in ballast, 75–100 mm thick on a compacted sub-base. Use 1:4 for a base that will carry a car or heavy machinery.
For concrete, about half a litre of water per kg of cement, so roughly 12 litres per 25 kg bag. Add it slowly: too much water makes weak concrete.
Unopened, usually a few months from the packing date printed on the bag. Once opened or damp, use it quickly. Lumpy cement should not be used.
No. Building sand is soft and fine, for mortar. Concrete needs ballast or sharp sand and gravel, and screed needs sharp sand.
Cement is taken at 1,440 kg per m³, sand at 1.6 and all-in ballast at 1.7 tonnes per m³, with dry-volume factors of 1.25 for concrete and 1.33 for sand and cement mixes. Mortar per m² of wall matches our brick and block calculators. Default prices are typical 2026 UK merchant prices and can be changed. Reviewed November 2026.