How Much Concrete Do I Need? Slabs, Footings & Post Holes
Published 15 November 2026 · DIY & Home
Try it nowConcrete Calculator →Ordering too little concrete is a disaster mid-pour; too much wastes money. Get exact quantities with the concrete calculator.
Slabs and footings
A 5 m × 4 m patio, 100 mm thick: 5 × 4 × 0.1 = 2 m³. Add 10% waste → 2.2 m³.
In imperial: 12 ft × 12 ft × 4 in = 48 ft³ = 1.78 cubic yards.
Post holes
10 holes, 300 mm wide and 600 mm deep: π × 0.15² × 0.6 × 10 ≈ 0.42 m³ (minus the posts’ own volume).
Bags or ready-mix?
- A 20 kg bag makes about 0.009 m³ – you’d need about 110 bags per m³.
- An 80 lb bag makes 0.6 ft³ – about 45 per cubic yard.
- Over about 1 m³, ready-mix delivery is usually cheaper and much easier.
Thickness guide
Paths 75–100 mm, sheds 100 mm, driveways 125–150 mm.
Keep reading
Novated leases can save thousands – especially on electric cars. Here is how the savings work and when they don’t.
15 Nov 2026Keep rent under 30% of income and convert weekly rents correctly – here is how to budget for your next place.
15 Nov 2026Locked-in certainty or flexible bonus interest? Here is how to choose between a term deposit and a savings account.
15 Nov 2026