Concrete grade
N20, N25, N32: the number is the characteristic compressive strength in MPa at 28 days. N20 is the minimum for residential footings under the NCC Housing Provisions.
Ask Chalkline about this →Concrete grade in Australia is expressed as a normal-class (N) grade followed by the characteristic compressive strength in megapascals (MPa) at 28 days. Common residential grades are N20, N25, N32, and N40. The higher the number, the stronger and more durable the mix.
Under the ABCB Housing Provisions 2022 Part 4.2, the minimum concrete grade for residential footings and slabs (including pad footings and strip footings) is N20 (20 MPa). In practice, most residential projects in 2026 specify N25 as the site minimum because N25 offers better durability on reactive or aggressive soil chemistry sites. Engineers routinely specify N32 or N40 for highly loaded elements or corrosive environments.
The grade is set at the batch plant and confirmed on the concrete docket. The docket records the grade, water-to-cement ratio, admixtures, and pour time. Keep the docket: it is evidence of compliance if a defect claim arises later.
Also known as: N-grade concrete, concrete strength grade, MPa grade.
Category: Materials.
Related
- Pad footings: construction and sizing for residential builds
- Slab on ground construction: residential build sequence
See also
Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.