How many 20 kg bags make a cubic metre
Pre-mixed concrete in Australia comes in 20 kg bags, and the makers don’t agree on what a bag makes. Their data sheets put a cubic metre at anywhere from 100 to 110 bags:
| Bag | Bags a cubic metre | Bunnings, 4 Oct 2026 |
|---|---|---|
| Australian Builders High Strength | about 100 | $9.90 |
| Easy Mix Concrete | 100 (0.01 m³ a bag) | — |
| Boral Concrete Mix | 108 | — |
| Dingo MaxPRO | 108 | $14.44 |
| Cement Australia PROSTRENGTH Rapid Set | about 110 | — |
The calculators start at 100 bags a cubic metre, with the $9.90 bag that states it, and let you pick 108 or 110 instead. A cubic metre is a lot of bags: 100 of them weigh 2 tonnes before any water goes in. Bastion’s $8.88 bag at Bunnings doesn’t state a yield, so it isn’t in the table.
Ordering ready-mix
Ready-mix is ordered by the cubic metre. Hunter Readymixed takes orders in steps of 0.1 m³, rounded up, and suggests allowing 10% for wastage on small jobs; the slab calculator does both.
Small loads cost extra. Boral’s fees for metropolitan New South Wales, from 4 May 2026, charge a load under 3 m³ as if the truck carried 3 m³: on a 2.0 m³ order, the missing 1.0 m³ is charged at $95, plus GST. Other suppliers and regions set their own fees, so ask when you get the quote. The slab calculator shows the fee Boral’s rule would add, so you can weigh it against the bags.
Concrete weighs about 2,400 kg a cubic metre, the figure Holcim gives for most concrete and the default in AS 3600. A 2 m³ pour is close to 5 tonnes, which is worth knowing before you barrow it.
Slabs, paths and driveways
Cement Concrete & Aggregates Australia’s data sheet on residential driveways and paths sets the minimum thickness by what will drive on the slab:
- 75 mm for foot traffic only, such as paths and patios.
- 100 mm for vehicles under 3 tonnes.
- 150 mm for vehicles of 3 to 10 tonnes.
It puts control joints no more than 3 m apart, with no panel more than 1.5 times as long as it is wide, and the mesh in the top half of the slab with at least 30 mm of concrete over it. The slab calculator counts the joints for you, and the mesh calculator lays out the sheets.
Post holes
Boral publishes a chart of 20 kg bags for common posts: two to three for a 75 mm post in a 250 mm hole 600 mm deep, up to four to five for a 100 mm post in a 300 mm hole 700 mm deep. For its rapid-set mix, Cement Australia puts about two bags in a post hole. The post hole calculator works out any hole and checks the result against Boral’s chart.
Questions people ask
How many 20 kg bags of concrete make a cubic metre?
Between 100 and 110, depending on the maker. Easy Mix and Australian Builders put it at about 100, Boral and Dingo MaxPRO at 108, and Cement Australia’s PROSTRENGTH Rapid Set at about 110. Check the bag you buy and pick its figure in the calculator.
How much does a cubic metre of concrete weigh?
About 2,400 kg. Holcim gives that figure for most concrete; it is also the default design value in AS 3600. The 100 to 110 bags it takes to make a cubic metre weigh 2,000 to 2,200 kg before water.
What is the smallest ready-mix order?
Suppliers deliver small loads but charge for them. Boral’s metropolitan NSW fees charge any load under 3 m³ as if it were 3 m³, at $95 a cubic metre short plus GST. Orders go in steps of 0.1 m³ at Hunter Readymixed. Ask your supplier for its own minimum.
How thick should a concrete driveway be in Australia?
At least 100 mm for cars and other vehicles under 3 tonnes, and 150 mm for vehicles of 3 to 10 tonnes, according to CCAA. Paths and patios that only take foot traffic can be 75 mm.
Which mesh do I need?
The one that suits the slab: CCAA asks for the mesh size to suit the slab’s thickness and joint spacing. Sydney Reo sells SL72 for driveways, patios, pavements and shed bases. House slabs and footings follow the NCC or an engineer’s design, so use the mesh on your plans.
Sources for the numbers on this page
- Building Products Supplies (Australian Builders) — High Strength Concrete 20 kg, product data sheet: about 100 bags make a cubic metre (PDF) · checked 4 October 2026
- River Sands (Easy Mix) — Easy Mix Concrete, data sheet (March 2020): 0.01 m³ a 20 kg bag · checked 4 October 2026
- Boral — Concrete Mix 20 kg, product data sheet (February 2022): 108 bags make a cubic metre · checked 4 October 2026
- Bunnings — Dingo 20kg MaxPRO Concrete Mix: 108 bags make a cubic metre ($14.44) · checked 4 October 2026
- Cement Australia — PROSTRENGTH Rapid Set Concrete, data sheet (April 2024): about 110 bags a cubic metre (PDF) · checked 4 October 2026
- Bunnings — Australian Builders 20kg High Strength Concrete Mix ($9.90) · checked 4 October 2026
- Bunnings — Bastion 20kg Concrete Mix ($8.88) · checked 4 October 2026
- Hunter Readymixed Concrete — Ordering concrete (in 0.1 m³ steps, with 10% for wastage on small jobs) · checked 4 October 2026
- Boral — Concrete service fees, NSW Metro (effective 4 May 2026): loads under 3 m³ · checked 4 October 2026
- Holcim Australia — Glossary: density of concrete and normal-class grades (N20 to N50) · checked 4 October 2026
- Cement Concrete & Aggregates Australia — Residential concrete driveways and paths, data sheet (August 2026, PDF) · checked 4 October 2026
- Sydney Reo Supplies — SL72 reinforcement square mesh, 6.0 m × 2.4 m sheet · checked 4 October 2026
- Boral — Post Hole Concrete Mix: 20 kg bags by post size, hole diameter and depth · checked 4 October 2026
- Cement Australia — Rapid Set Concrete, sell sheet (December 2021): about two 20 kg bags a post hole (PDF) · checked 4 October 2026
Corrections and updates are logged on the sources page.