Cost Guide
Concrete Slab Cost: Per m², Per m³ & Shed Slabs (2026)
By Mount Gambier Concrete · 12 July 2026
Quick answer
As a 2026 Australian guide, a plain concrete slab costs roughly $80–$150 per square metre supplied and laid, and concrete itself is around $250–$350 per cubic metre delivered. A typical 6x6m (36 m²) shed slab therefore usually lands around $3,000–$5,500 depending on thickness, reinforcement and site prep. Engineered house slabs cost more and are quoted to the plans. Always get an itemised written quote.
Whether you’re putting up a shed, building a home, adding a carport or pouring a floor for a farm building, the slab is the foundation everything else depends on. And like any foundation, it pays to get it right — and to understand what it costs before you commit.
This guide explains concrete slab costs in Australia in 2026, both per square metre and per cubic metre, and what makes the price change. As always, we won’t quote a single fixed “average” — every slab is different — but you’ll know exactly what you’re paying for.
On the Limestone Coast the ground under your slab has a big say in the final price. The shallow limestone and free-draining karst around Mount Gambier, the reactive terra rossa red soils inland at Naracoorte, Penola and Coonawarra, the soft drained flats near Millicent and Tantanoola, and the salty coastal air at Port MacDonnell and Robe all change how a slab needs to be designed and built. That’s why the same shed slab can be quoted differently across the region — and why a site assessment matters more than any per-metre average you’ll read online.
Concrete slab cost per square metre
Most slabs are priced per square metre, supplied and laid, which bundles the concrete, reinforcement, labour and finishing into one figure:
| Slab type | Indicative cost (supplied & laid) |
|---|---|
| Plain shed / garage slab | $80 – $120 per m² |
| Reinforced / thicker slab | $100 – $150 per m² |
| Engineered house slab | Quoted to the plans (often $120 – $180+ per m²) |
For a common 6 x 6 metre (36 m²) shed slab, that typically works out around $3,000–$5,500 depending on thickness, reinforcement and how much site prep is needed.
Ballpark totals by slab size
To help you sanity-check a budget before you get a quote, here’s how the per-square-metre rate scales across common sizes. These assume a standard reinforced slab on a reasonable site — treat them as indicative, not a price:
| Slab | Area | Indicative range |
|---|---|---|
| Small shed / garden studio (3 x 3m) | 9 m² | ~$900 – $1,400 |
| Single garage / carport (6 x 3m) | 18 m² | ~$1,600 – $2,700 |
| Standard shed (6 x 6m) | 36 m² | ~$3,000 – $5,500 |
| Large shed / workshop (9 x 7m) | 63 m² | ~$5,500 – $9,500 |
| Machinery / farm shed (12 x 9m) | 108 m² | ~$9,000 – $16,000+ |
Notice the per-square-metre rate tends to improve on bigger, simpler pours, because the fixed costs — getting the truck and crew on site, setting up formwork, cutting joints — are spread across more area. A tiny slab can feel expensive per metre for exactly that reason.
Concrete cost per cubic metre
You’ll also see concrete priced per cubic metre (m³) — that’s the raw, delivered price of the concrete itself, before labour, reinforcement and finishing. As a 2026 guide, ready-mix concrete is around $250–$350 per cubic metre delivered, varying with the mix strength (e.g. 20, 25 or 32 MPa), how far it’s carted, and any small-load or short-load fees.
To picture volume: a 36 m² slab at 100mm thick uses about 3.6 cubic metres of concrete. The per-m³ price matters, but on most jobs the labour, base prep, formwork and steel are just as significant as the concrete itself — which is why the per-square-metre “supplied and laid” figure is the more useful number for budgeting.
A quick way to estimate concrete volume
If you want to rough out how much concrete a slab needs yourself, the formula is simply length × width × thickness (all in metres). A 6 x 6m slab at 0.1m (100mm) thick is 6 × 6 × 0.1 = 3.6 m³. Bump the thickness to 125mm and it’s 4.5 m³; at 150mm it’s 5.4 m³. Always allow a little extra for uneven ground and edge thickenings — most concreters order slightly over to avoid running short mid-pour, because a second, small “short load” delivery is both slow and expensive. This is one reason getting the base level and the formwork right saves money: it keeps the volume predictable.
Why mix strength matters
That per-cubic-metre figure moves with the concrete’s strength, quoted in megapascals (MPa). A domestic shed slab is commonly poured in 20–25 MPa, while slabs carrying heavier loads, or exposed to aggressive conditions like coastal salt near Port MacDonnell or Robe, may be specified at 32 MPa or higher. Stronger mixes cost a little more per cubic metre but buy durability where it’s needed. Your engineer or concreter will nominate the right strength — it’s not somewhere to cut corners, especially on a reactive site.
What changes the price
Thickness
A typical domestic shed or garage slab is 100mm thick. Where heavy machinery, vehicles, hoists or structural loads are involved, we thicken the slab and add reinforcement — more concrete, more steel, higher cost, but essential for the loads.
Reinforcement
Steel mesh is standard; heavier bar reinforcement, extra beams or engineered thickenings add cost. On a house slab the reinforcement is specified by an engineer and is non-negotiable.
Site preparation
Excavation, building up and compacting the base, a moisture barrier, and dealing with slope or soft ground all take time and materials. On a sloping or difficult site, prep can be a big part of the total.
This is where the Limestone Coast’s varied ground shows up on the invoice. Around Mount Gambier, shallow limestone can give you a naturally firm base — occasionally you’ll need some rock breaking, but often the ground is a good starting point, and the free-draining karst means less trouble with trapped water. Inland at Naracoorte, Penola and Coonawarra, the reactive terra rossa red soils expand and contract with moisture; slabs there benefit from proper base preparation and reinforcement (and often an engineer’s input) so the slab moves as one and doesn’t crack. On the soft, drained flats near Millicent and Tantanoola, expect more spend on building up and compacting a stable base — skip it and the slab can settle unevenly later. It’s cheaper to do this once than to fix a sunken slab.
Moisture barrier and drainage
Under a slab that will become a floor, a plastic vapour barrier is standard to stop ground moisture wicking up into the concrete — essential if you’ll ever polish the slab, lay flooring, or store moisture-sensitive gear. Getting drainage and falls right also protects the slab, and around Mount Gambier it protects the aquifer below by keeping surface water managed. These are small line items that prevent big problems.
Access
If a truck can back up to the pour, it’s quick. If concrete has to be pumped or barrowed a long way, that’s extra labour. For big or awkward pours we use concrete pumping.
Finish
A basic shed slab gets a plain trowel finish. If you want a polished or decorative finish on the slab, that adds cost — but gives you a finished floor in one go.
Shed slab, house slab or footings — what do you need?
- Shed / garage slab: usually a thickened-edge slab, poured to fit your shed kit. Send us the kit dimensions and we’ll set it out to suit.
- House slab: an engineered waffle-pod or raft slab poured to the plans, working in with your builder and building surveyor.
- Footings: strip, pad or pier footings for extensions, retaining or structures — often quoted alongside the slab.
What a proper slab quote includes
Like a driveway, a slab that lasts is mostly about the parts you can’t see once it’s poured. A fair fixed-price quote should spell out:
- Excavation and removal of spoil to get to the right level
- Base preparation — building up and compacting a stable sub-base
- A vapour barrier / moisture membrane where the slab is a floor
- Formwork set to line and level, including any thickened edges
- Steel reinforcement — mesh, bar, or engineered beams as specified
- The concrete at the right strength and thickness
- Finishing — trowel, broom, or a decorative finish
- Control or saw-cut joints to manage shrinkage cracking
- Clean-up and site tidy on completion
If one quote is dramatically cheaper than the others, look for what’s been left out — usually it’s the base prep, the membrane, or the reinforcement. Those omissions don’t save you money; they defer the cost to when the slab cracks or lifts.
How to keep a slab budget sensible
- Send accurate dimensions. For a shed slab, your kit’s setout drawing tells us exactly what to form up, avoiding a slab that’s bigger (and dearer) than it needs to be.
- Pour it once at the right thickness. Under-building to save on concrete is a false economy if the slab will carry a hoist, a vehicle or machinery.
- Combine jobs where it makes sense. If you’re doing a shed slab and a nearby driveway or path around the same time, one mobilisation can be more efficient than two.
- Get the finish you’ll actually use. A plain trowel finish is fine for a shed floor; only pay for a polished or exposed aggregate finish where it earns its keep.
Common questions
Is it cheaper to pour a slab in one go or in sections? For most residential jobs, a single continuous pour is both cheaper and stronger than pouring in sections, because it avoids cold joints and repeated setup. Very large commercial slabs are sometimes poured in planned bays for practical reasons.
How thick should my shed slab be? 100mm is standard for a domestic shed or garage. Go thicker (125–150mm) with added reinforcement if you’ll park heavy vehicles, run machinery, or install a hoist. The slab and thickness guide covers this in more detail.
Do I need an engineer? House slabs and any slab carrying structural or heavy loads should be engineered, particularly on reactive terra rossa soils inland. A simple garden-shed slab usually doesn’t. We’ll tell you which camp your job falls into.
How long before I can build on it? You can typically start light work within a few days, but concrete keeps gaining strength for weeks. See how long concrete takes to cure before loading or building on a new slab.
Why is my small slab so expensive per square metre? Fixed costs — delivery, setup, formwork, joint cutting — don’t shrink much on a small pour, so they spread over fewer metres. That’s normal, not a markup.
Get the number for your slab
Slab cost comes down to size, thickness, reinforcement, prep and finish — which is why a written quote beats any online average. Send us your shed kit dimensions or plans and we’ll set out and quote your slab as a fixed price.
Ready for a real figure? Call 0400 123 456 or get a free quote for your shed, house or machinery slab — across Mount Gambier and the Limestone Coast. Also see how long concrete takes to cure before you load or build on it.