Raft Slab Calculator
Get an instant price estimate for a standard residential raft slab, based on your project area, slab thickness and whether bored piers are required.
Raft Slab Calculator
Estimate the cost of a standard residential raft slab.
Standard Price Includes
- ✓ Reinforcement
- ✓ Concrete Supply
- ✓ Labour
- ✓ Slab Concrete Pump
- ✓ Site Cut
- ✓ Base Preparation
- ✓ Trench Depth up to 500 mm
Estimating A Raft Slab For A Melbourne Home
A raft slab is a single, thickened concrete slab reinforced to spread the load of the building evenly across the ground beneath it. It is generally a simpler, more economical design than a waffle slab and suits sites with more stable soil conditions. This calculator gives you a fast, standard-rate estimate for a typical residential raft slab, using the same pricing structure HPL Construction uses to quote real projects.
The base cost is your project area in square metres multiplied by a standard rate of $180 per square metre (ex GST), which covers reinforcement, concrete supply, labour, the slab concrete pump, site cut, base preparation and trench depth up to 500 mm. Upgrading from the standard 110 mm slab to a 140 mm slab adds a flat $2,000 to cover the extra concrete and reinforcement.
Adding Bored Piers
Where a soil report calls for deeper footings, bored piers can be added to a raft slab in the same way as a waffle slab. Enter the number of piers and their average depth, and the calculator works out the extra concrete volume for a standard 450 mm diameter pier (using π × radius² × depth) at $200 per cubic metre, plus excavation, pouring and pump costs on the same basis as our other slab calculators.
What Information You Need To Enter
Enter your slab area in square metres, choose between 110 mm and 140 mm thickness, and indicate whether bored piers are required. If they are, add the pier quantity and average depth — both usually specified in your soil report or engineering drawings.
Understanding Your Results
You will see the standard raft slab cost, any thickness upgrade, bored pier costs where applicable, a subtotal, GST at 10 per cent, and a total inclusive of GST. As with our other slab calculators, this assumes standard site conditions and does not include step-downs, deep edge rebates, retaining walls, suspended slabs, difficult access or imported fill.
Why Accurate Estimating Matters
A realistic raft slab estimate lets you compare it against a waffle slab for your site, plan your overall build budget, and understand roughly what a thickness upgrade or bored piers will add before you receive a formal quote.
Frequently Asked Questions
What is a raft slab and when is it used?
A raft slab is a single, thickened, reinforced concrete slab that spreads building load evenly across the ground. It suits sites with more consistent, less reactive soil, and is often a more cost-effective option than a waffle slab where soil conditions allow.
Raft slab or waffle slab -- which is right for my site?
This depends on your soil classification, which is determined by a geotechnical soil report. Raft slabs generally suit less reactive soil, while waffle slabs are more common on reactive clay. We can help confirm which applies to your site.
What does the 140 mm upgrade include?
The 140 mm option increases the overall slab thickness and reinforcement compared with the standard 110 mm slab, generally specified where a soil report or engineering assessment calls for additional slab stiffness.
Are bored piers common with raft slabs?
They can be required on sites with variable bearing conditions or where a raft slab alone does not provide adequate support at certain points. Your soil report and engineering drawings will confirm if piers are needed.
Is trench depth included in the estimate?
Yes, the standard estimate includes trench depth up to 500 mm. Deeper trenching required by your site or engineering drawings would be confirmed and priced separately.
Related Calculators & Services
Need An Exact Price, Not Just An Estimate?
The Raft Slab Calculator gives you a fast, useful planning figure. For a fixed, accurate price backed by a site assessment, request a free professional quotation from HPL Construction.
