Ballast and Cement Calculator
Find how much ballast and cement you need, or how much cement goes with the ballast you have.
Measure your job
Your answer
For 0.39 m³ of concrete, mixed 1 : 5 ballast.
Bulk bags are 800 kg. Bags are rounded up.
This answer is a guide. For footings, walls or anything that holds weight, check your local building rules or ask a builder or engineer.
Which costs less?
But you do all the mixing. Hire a mixer for big jobs.
UK middle prices from October 2026, with VAT. Cement: £8.39 a 25 kg bag (7 prices from 3 sellers). Bulk bags: £75, building sand £67.35 (3 sellers each). Few prices, so treat them as a rough guide.
Quick answers
- 1 tonne of ballast at 1 : 6
- About 6.3 bags of 25 kg cement, by British Standard figures.
- An 800 kg bulk bag at 1 : 6
- About 5.1 bags of cement. It makes about 0.43 m³ of concrete.
- A 2.5 × 1.9 m shed base
- At 75 mm and 1 : 5, with 10% extra: 6 bags of cement and 719 kg of ballast.
- Small bags of ballast
- Wickes sells 22.5 kg bags at £4.10 with VAT. One bag of cement does about 6.2 of them at 1 : 5.
How to work it out
- Work out the m³ of concrete: length × width × depth, in metres.
- Add 10% extra for spills.
- Multiply by the ballast for your mix: 1,835 kg per m³ at 1 : 5.
- Multiply the m³ by the cement: 330 kg per m³ at 1 : 5.
- Divide the cement by 25 for bags, and the ballast by 800 for bulk bags. Round up.
Shed base 2.5 × 1.9 × 0.075 = 0.356 m³ + 10% = 0.392 m³
Ballast: 0.392 × 1,835 = 719 kg → 1 bulk bag
Cement: 0.392 × 330 = 129 kg ÷ 25 → 6 bags
Cement per tonne or bulk bag of ballast
Already have ballast? Find its weight in the first column. Then read across to your mix for the bags of cement.
| Ballast | 1 : 6 | 1 : 5 | 1 : 4 |
|---|---|---|---|
| 1 tonne | 6.3 (158 kg) | 7.2 (180 kg) | 8.3 (208 kg) |
| 800 kg bulk bag | 5.1 (127 kg) | 5.8 (144 kg) | 6.7 (167 kg) |
| 850 kg bulk bag | 5.4 (134 kg) | 6.1 (153 kg) | 7.1 (177 kg) |
| 22.5 kg small bag | 0.14 (3.6 kg) | 0.16 (4 kg) | 0.19 (4.7 kg) |
Bags of cement, with the kg in brackets. From the British Standard table (BS 8500-2). Buy whole bags, so round up.
A mix of 1 : 5 means 1 part cement to 5 parts ballast. The parts are measured by volume, such as buckets.
The 850 kg row is for sellers such as Mainland Aggregates, whose bulk bags hold that much.
Concrete from a tonne or an 800 kg bag of ballast
| Ballast | 1 : 6 | 1 : 5 | 1 : 4 |
|---|---|---|---|
| 1 tonne | 0.54 m³ | 0.54 m³ | 0.56 m³ |
| 800 kg bulk bag | 0.43 m³ | 0.44 m³ | 0.44 m³ |
| 850 kg bulk bag | 0.46 m³ | 0.46 m³ | 0.47 m³ |
By the British Standard table: the richer the mix, the less ballast in each m³.
Mainland Aggregates, a merchant, says an 850 kg bulk bag makes about 0.5 m³. By our sums, it is about 0.46 m³ at 1 : 6.
Ballast and cement for 1 m³ (a cube) of concrete
At 1 : 6: 1,865 kg of ballast and 295 kg of cement (12 bags). At 1 : 5: 1,835 kg and 330 kg (14 bags). Our cement calculator lists every mix.
Ballast and cement for a shed base
Heidelberg Materials lays a shed base at least 75 mm thick, 100 mm bigger than the shed. It mixes 1 part cement to 5 parts ballast. B&Q's guide uses 1 : 4.
| Shed | Base | Cement bags | 800 kg bags | Or 22.5 kg bags |
|---|---|---|---|---|
| 6 × 4 ft | 1.93 × 1.32 m | 3 | 1 | 18 |
| 8 × 6 ft | 2.54 × 1.93 m | 6 | 1 | 33 |
| 10 × 8 ft | 3.15 × 2.54 m | 9 | 2 | 54 |
Shed sizes in feet, worked out in metres. Ballast as bulk bags or small bags.
Would you rather use ready-to-use bags? Our concrete slab calculator counts them for any base.
Buying ballast and cement
- Cement: about £8.39 a 25 kg bag with VAT, the middle of 7 prices from 3 sellers.
- Bulk bag of ballast: about £75 with VAT, the middle of only 3 sellers. That is £94 a tonne.
With so few sellers, treat these prices as a rough guide. For small bags, and what a bulk bag of ballast covers, see our ballast calculator.
The British Standard allows all-in ballast only up to ST3, our 1 : 6. The 1 : 5 and 1 : 4 columns use the ST4 and ST5 amounts as a guide. For a stronger mix, see our cement calculator. For footings, drives or anything that holds weight, check your local building rules or ask a builder or engineer.
Questions people ask
How much ballast and cement do I need?
Work out the m³ of concrete and add 10%. For each m³ at 1 : 5, where the calculator starts, use 1,835 kg of ballast and 330 kg of cement. That cement is 13.2 bags of 25 kg.
How many bags of cement to a tonne of ballast?
About 6.3 bags of 25 kg at 1 : 6. A richer mix takes more: 7.2 at 1 : 5 and 8.3 at 1 : 4.
How much cement do I mix with ballast?
Sources differ. Heidelberg's cement data sheet uses 1 part cement to 4 parts ballast, by volume. Its shed base guide uses 1 : 5. By weight, 1 : 5 is about 7.2 bags of cement per tonne of ballast.
How much concrete will a tonne of ballast make?
About 0.54 m³ at 1 : 6, by British Standard figures. An 800 kg bulk bag makes about 0.43 m³.
How much ballast and cement for a shed base?
Take a 2.5 × 1.9 m base, 75 mm thick, at 1 : 5. It needs about 719 kg of ballast and 6 bags of cement, with 10% extra.
How much ballast and cement per square metre?
At 75 mm thick and 1 : 5: about 138 kg of ballast and 25 kg of cement for each m². At 100 mm: 184 kg and 33 kg.
What does it cost to mix a bulk bag of ballast?
About £125 with VAT: one bulk bag at £75 and 6 bags of cement at £8.39. At 1 : 6, it makes about 0.43 m³.
Where our numbers come from
- Cement and stone per m³: BS 8500-2 Table 10 (as copied by Pavingexpert)
- Mix ratios and 25 kg bags: Heidelberg General Purpose cement data sheet
- Shed base: Heidelberg Materials guide (75 mm concrete minimum)
- Shed base: B&Q guide (75 mm concrete on 75 mm Type 1)
- Mainland Aggregates: 850 kg bulk bags
- Ballast weight: Wickes ballast bulk bag (800 kg covers 9.7 m² at 50 mm)
- Ballast small bag: Wickes 22.5 kg Major Bag £4.10
- Cement price: the middle of 7 prices from 3 UK sellers (25 kg, Oct 2026)
- Bulk bag prices: the middle price from 3 UK sellers each (Wickes, Tippers, Lawsons; Oct 2026)
- Bag price: the middle of 4 prices from 3 UK stores for 20 kg concrete (Oct 2026)
- Bag size: Blue Circle Multi-Purpose Concrete data sheet (20 kg makes about 0.01 m³)
- Ready-mix price: the middle of 7 prices from 4 UK suppliers (Oct 2026, with VAT)
- Rock Solid Concrete price guide (Midlands ready-mix)
- Extra for spills: Sakrete slab calculator (10%)
- Unit sizes: NIST Handbook 44, Appendix C (1 ft = 0.3048 m; 1 US gallon = 231 cubic inches)
Made by BuildersCount. Last checked 4 Oct 2026.
How we work out our numbers About us Found a mistake? Tell us