Concrete Bag Calculator
Find how many 20 kg bags of concrete you need, and what they will cost.
Measure your project
Your answer
That makes 0.11 m³. We added 10% extra.
If you buy bags
Blue Circle says each 20 kg bag makes about 0.01 m³ (10 litres).
If you order a lorry (ready-mix)
Ask for 1.00 m³. Rock Solid Concrete takes home orders from 1 m³, so we price at least that.
This is a guide. For footings, drives or anything that holds weight, check your local building rules or ask a builder or engineer.
Which costs less?
But you must mix 11 bags by hand. That is 220 kg to lift.
UK middle prices from October 2026, with 20% VAT. Bags: 4 prices from 3 stores.
Quick answers
- A 1 × 1 m pad, 100 mm thick
- 11 bags of 20 kg, with 10% extra. That is about £121 at our middle price.
- What one bag makes
- About 0.01 m³, or 10 litres, says Blue Circle.
- What one bag covers
- About 0.1 m² at 100 mm thick. That is a square about 32 cm each side.
- Water per bag
- About 2 litres for each 20 kg bag, says Blue Circle.
- Price
- About £11 a bag with VAT. It is the middle of 4 prices from 3 UK stores.
How to work it out
- Work out the volume in m³: length × width × thickness, all in metres.
- Add 10% extra for spills.
- Divide by 0.01, what one 20 kg bag makes.
- Round up to the next whole bag.
- Multiply the bags by the price of one bag for the cost.
1 × 1 × 0.1 = 0.1 m³
0.1 + 10% = 0.11 m³
0.11 ÷ 0.01 = 11 → 11 bags
11 × £11 = £121
What one 20 kg bag of concrete makes
Ready-to-use concrete comes dry in a bag, or sack. You add only water.
Blue Circle says one 20 kg bag of its multi-purpose concrete makes about 0.01 m³. That is 10 litres, or a block 0.33 × 0.33 × 0.1 m.
We use that figure for all 20 kg bags. We could not find what other brands' bags make.
Other bag sizes
- 25 kg bags: we found no UK maker's figure for a 25 kg bag of concrete.
- 10 kg tubs: Blue Circle sells them but gives no figure. Half a 20 kg bag would be about 0.005 m³.
- Post mix: for fence posts only. Our fence post concrete calculator counts those bags.
How many bags of concrete for small jobs
| Job | m³ (+10%) | Bags | Cost |
|---|---|---|---|
| Pad 0.6 × 0.6 m, 100 mm thick | 0.040 | 4 | £44 |
| Pad 1 × 1 m, 100 mm thick | 0.110 | 11 | £121 |
| 4 round holes, 250 mm wide, 750 mm deep | 0.162 | 17 | £187 |
| Footing 3 m long, 450 mm wide, 150 mm thick | 0.223 | 23 | £253 |
| Pad 2 × 2 m, 100 mm thick | 0.440 | 44 | £484 |
Bags at £11 each with VAT, our middle price.
Add up your own job in the calculator above. Tap "Add another part" for each pad, hole or strip.
When bags cost less than a lorry
Bags cost far more per m³, but a ready-mix lorry has a smallest order and may add fees. This table shows the most bags you can buy before a lorry costs less.
| Lorry charge | Bags | Concrete |
|---|---|---|
| 1 m³ at £150, no fees | 13 bags | 0.13 m³ |
| Plus a £100 delivery fee | 22 bags | 0.22 m³ |
| Plus a £200 delivery fee | 31 bags | 0.31 m³ |
| A £750 minimum charge | 68 bags | 0.68 m³ |
Bags at £11. Lorry at our middle price of £150 per m³ with VAT. Delivery fees are Checkatrade's range (it does not say if VAT is in). The minimum charge is Mister Concrete's (£625 plus VAT).
Ask your supplier for their smallest order and fees. Then type them into "Change prices" above.
Mixing your own
One 800 kg bulk bag of ballast makes about 0.43 m³ of concrete. That is at 1 : 6 ballast, by the British Standard figures. It needs about 5.1 bags of cement. That is as much as 43 ready-to-use bags.
Our ballast and cement calculator works it out.
Mixing bagged concrete
- Add about 2 litres of clean water to each 20 kg bag, says Blue Circle.
- In a mixer, mix for 3–5 minutes.
- Use it within 30 minutes.
- Don't use it below 5 °C or above 30 °C unless you protect the work.
- Cover the new concrete for at least 7 days.
Hanson's bags (Maxipacks) are 20 kg, says a Heidelberg data sheet. So a pallet of 56 weighs about 1,120 kg. Check how it will reach your job.
Questions people ask
How many bags of concrete do I need?
Find the m³, add 10%, then divide by 0.01 for 20 kg bags. A 1 × 1 m pad, 100 mm thick, takes 11 bags.
How many m³ is a 20 kg bag of concrete?
About 0.01 m³, which is 10 litres. Blue Circle says one bag fills a block about 0.33 × 0.33 × 0.1 m.
How much does a 20 kg bag of concrete cover?
About 0.1 m² at 100 mm thick, or 0.13 m² at 75 mm. Thinner concrete covers more.
How much concrete does a 10 kg bag make?
Blue Circle sells 10 kg tubs but gives no figure for them. If a tub makes half what a 20 kg bag makes, that is about 0.005 m³.
How much is a bag of concrete?
About £11 for 20 kg, with VAT. Prices ran from £9.99 to £11.80 at 3 stores. Wickes also had 10 for £100.
How much water do you add to a 20 kg bag of concrete?
About 2 litres of clean water per bag, says Blue Circle. Mix for 3–5 minutes in a mixer, and use it within 30 minutes.
How many bags of concrete are on a pallet?
In its 2021 guide, Hanson packed its 40N concrete 56 bags to a pallet. Its multi-purpose bag was 60 to a pallet, but was marked not on sale. We found no other maker's count.
Can I use post mix as normal concrete?
No. Blue Circle says Postcrete is not for general concreting. It is for setting posts, and sets in 5–10 minutes.
Where our numbers come from
- Bag size: Blue Circle Multi-Purpose Concrete data sheet (20 kg makes about 0.01 m³)
- Bag price: the middle of 4 prices from 3 UK stores for 20 kg concrete (Oct 2026)
- Ready-mix price: the middle of 5 prices from 3 UK suppliers (Oct 2026, with VAT)
- Rock Solid Concrete price guide (Midlands ready-mix)
- Ready-mix delivery and minimum order: Checkatrade cost guide (a third party)
- Minimum charge: Mister Concrete price page (£625 + VAT)
- Hanson packed products guide (2021): bags per pallet
- Post holes: Blue Circle Postcrete data sheet (bags per hole)
- Cement and stone per m³: BS 8500-2 Table 10 (as copied by Pavingexpert)
- Ballast weight: Wickes ballast bulk bag (800 kg covers 9.7 m² at 50 mm)
- Mix ratios and 25 kg bags: Heidelberg General Purpose cement data sheet
- Ready-mixed mortar bags: Heidelberg Sand & Cement Mortar data sheet (20 kg lays about 19 bricks)
- Full loads, barrows and mixes: Heidelberg Materials UK merchant guide
- Extra for spills: Sakrete slab calculator (10%)
Made by BuildersCount. Last checked 4 Oct 2026.
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