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Work out how much cement, sand and gravel, or all-in ballast, you need for a concrete mix such as 1:2:4. Pick the mix, enter how much concrete you need and press Calculate to see the bags, tonnes, water and how many buckets go with each bag of cement.
| Mix | Strength | Cement Bags | Sand + Gravel | Cost |
|---|
Typical 2026 UK prices including VAT, in bulk bags, or 20 kg bags for small amounts. Your mix is highlighted.
You get the bags of cement, the tonnes and bulk bags of sand and gravel or ballast, the water, how many buckets of each go with every bag of cement, and the cost of all four mixes side by side.
A mix ratio is the amount of each dry material by volume, always starting with cement. In a 1:2:4 mix, every bucket of cement goes with two buckets of sharp sand and four buckets of gravel. The more sand and gravel for each part of cement, the weaker and cheaper the concrete.
| Mix (cement : sand : gravel) | All-in ballast | Rough strength | Typical use |
|---|---|---|---|
| 1:1.5:3 | 1:4 | About C25 | Driveways, garage floors, structural work |
| 1:2:4 | 1:5 | About C20 | Slabs, shed bases, paths, house footings |
| 1:2.5:5 | 1:6 | About C15 | Foundations for garden walls, bedding |
| 1:3:6 | 1:8 | About C10 | Blinding, kerb and post bedding, fill |
The strength classes are only a guide: different sources put the same ratio a grade apart, because a site mix depends on how well it is measured, the sand, the water and the curing. Where the strength really matters, order ready-mix to the grade on the drawings.
| Mix | Cement | Sharp sand | 20 mm gravel |
|---|---|---|---|
| 1:1.5:3 | 403 kg (16.1 bags) | 0.67 t | 1.34 t |
| 1:2:4 | 317 kg (12.7 bags) | 0.70 t | 1.41 t |
| 1:2.5:5 | 261 kg (10.4 bags) | 0.72 t | 1.45 t |
| 1:3:6 | 222 kg (8.9 bags) | 0.74 t | 1.48 t |
The dry materials take up about 1.54 times the volume of the finished concrete, because the sand and cement fill the gaps between the stones and the mix packs down when it is wet. For 1 m³ of 1:2:4, that is 1.54 m³ of dry materials, split into 7 parts: 0.22 m³ of cement, 0.44 m³ of sand and 0.88 m³ of gravel.
All-in ballast, also called combined aggregate, is sand and gravel already mixed, usually 20 mm down to dust. It saves buying and storing two materials, and it is how most builders mix small amounts of concrete. Because it is already blended, it packs more tightly than separate sand and gravel, so the mix is written as cement to ballast.
| Ballast mix | Similar to | Cement | All-in ballast |
|---|---|---|---|
| 1:4 | 1:1.5:3 | 360 kg (14.4 bags) | 1.70 t |
| 1:5 | 1:2:4 | 300 kg (12 bags) | 1.77 t |
| 1:6 | 1:2.5:5 | 257 kg (10.3 bags) | 1.82 t |
| 1:8 | 1:3:6 | 200 kg (8 bags) | 1.89 t |
These use the same figures as our ballast calculator and cement calculator. Ballast varies from pit to pit; if a batch looks short of fine material, it can need a little extra sand.
On site, concrete is measured with a bucket or a shovel, never weighed. A 25 kg bag of cement is about 17 litres, which is roughly 1¼ of a standard 14-litre builder's bucket. So for each bag of cement in the mixer you add:
| Mix | Sharp sand | Gravel | Or all-in ballast |
|---|---|---|---|
| 1:1.5:3 | 2 buckets | 3½ buckets | 5 buckets (1:4) |
| 1:2:4 | 2½ buckets | 5 buckets | 6 buckets (1:5) |
| 1:2.5:5 | 3 buckets | 6 buckets | 7½ buckets (1:6) |
| 1:3:6 | 3½ buckets | 7½ buckets | 10 buckets (1:8) |
Fill the buckets level, not heaped, and use the same bucket for everything. A half-bag mixer takes about half a bag of cement with half these amounts, and a full bag batch makes about 0.08 m³ of concrete.
Use about half as much water as cement by weight: around 12 litres for each 25 kg bag. Add it gradually, as damp sand already holds some water. The concrete should hold its shape on a shovel and slump a little, not run. Extra water makes concrete easier to place but weaker, more prone to cracking and dusty on top, so add a plasticiser rather than more water if it is too stiff.
| Job | Mix | Notes |
|---|---|---|
| Garden path, shed base, patio | 1:2:4 or 1:5 ballast | On a compacted sub-base |
| Driveway, garage floor | 1:1.5:3 or 1:4 ballast | Ready-mix C25/30 or stronger is better |
| Strip footing for a house extension | Ready-mix to the drawings | Building Control checks the grade |
| Garden wall foundation | 1:2.5:5 or 1:6 ballast | Concrete at least 150 mm thick |
| Fence posts | 1:3:6, or post mix | Or a bag of rapid-setting post mix per post |
| Blinding under a slab | 1:3:6 or 1:8 ballast | A thin levelling layer only |
The gov.uk Approved Document A covers foundations for buildings. For how much concrete a job needs, start with our concrete calculator and bring the volume back here.
Sand and gravel: dry volume = concrete × 1.54 · each material = dry volume × its parts ÷ total parts
All-in ballast: dry volume = concrete × 1.25 · cement = dry ÷ (1 + n) · ballast = dry × n ÷ (1 + n)
Cement (kg) = volume × 1,440 · Sand and gravel (t) = volume × 1.6 · Ballast (t) = volume × 1.7
Cement is rounded up to whole 25 kg bags and the rest to 850 kg bulk bags, or 20 kg bags below 0.3 tonnes. Water is 0.5 litres per kg of cement. Prices are typical 2026 UK merchant prices including VAT: cement £7.50 a bag, sharp sand £65, 20 mm gravel £75 and ballast £70 a bulk bag.
The everyday UK mix is 1:2:4: one part cement, two parts sharp sand and four parts gravel by volume, or 1:5 cement to all-in ballast. Use 1:1.5:3 for stronger work and 1:3:6 for bedding and blinding.
About 12.7 bags (317 kg) for a 1:2:4 mix with sand and gravel, or 12 bags (300 kg) for 1:5 with all-in ballast. A stronger 1:1.5:3 mix takes about 16 bags.
Roughly C20, though a site mix varies with the sand, water and how carefully it is measured. Order ready-mix when you need a certified strength.
Not quite. Because all-in ballast packs more tightly than separate sand and gravel, 1:2:4 is closer to 1:5 cement to ballast. 1:6 ballast is nearer 1:2.5:5.
For 1:2:4, about 2½ buckets of sharp sand and 5 buckets of gravel per 25 kg bag, using 14-litre buckets. With all-in ballast at 1:5, about 6 buckets.
About 12 litres per 25 kg bag of cement, added gradually. Damp sand already holds water, so you may need less.
A strong mix, 1:1.5:3 or 1:4 with ballast, or better still ready-mix of C25/30 or stronger. Use at least 100 mm, or 150 mm for heavier vehicles.
No. Use sharp sand, which is coarser and gives a stronger, less crack-prone concrete. Soft building sand is for bricklaying mortar.
Dry volume factors of 1.54 for separate sand and gravel and 1.25 for all-in ballast, cement at 1,440 kg/m³, sand and gravel at 1.6 t/m³ and ballast at 1.7 t/m³, as used across ConstructionMath. Strength classes are approximate for nominal site mixes. Reviewed November 2026.