Estimate how much concrete to supply for a slab, patio, path, footing, round pad or fence-post project, then compare ready-mix and 20 kg bag supply costs. Enter your own metric measurements, add a practical waste allowance, compare the quantity with 20 kg bag yield and enter a current local A$/m³ rate for a concrete-only budget.
Select the shape that best matches the pour. Every numeric field starts visually at 0, but the 0 is only a placeholder. When you type a number, it replaces the placeholder instead of being added after it.
Zero-entry behaviour: the faded 0 is only a placeholder. The field itself is empty, so typing 5 gives 5 — not 05. Reset returns fields to the same empty-with-placeholder state.
Your result will appear after you enter measurements and press Calculate Concrete Supply.
Confirm final dimensions, mix specification, delivery access, minimum-load rules, approvals and supplier charges before ordering.
A rectangular concrete pour needs length, width and depth. Keep all three dimensions in metres before multiplying. When thickness is measured in millimetres, divide by 1000 first.
The tool separates the raw geometric volume from waste, bags and cost so you can see exactly which assumptions are changing the final planning quantity.
Calculate cubic metres for common residential and landscaping shapes.
Add your own contingency rather than relying on a fixed percentage.
Use the exact manufacturer yield in litres for bagged-concrete planning.
Enter your own current supplier quote instead of relying on a hard-coded price.
Save the estimate with measurements, waste, bags and concrete-only cost.
The visual zero is a placeholder only, so new typing replaces it automatically.
A reliable concrete estimate starts with volume, not with a guess about truck size or the number of bags. For a rectangular slab, patio, shed base or path, measure the finished internal length and width of the formed area, then multiply those dimensions by the concrete thickness. Because concrete thickness is commonly recorded in millimetres in Australia, convert the thickness to metres before multiplying. A 100 mm thickness is 0.10 m, 125 mm is 0.125 m and 150 mm is 0.15 m.
The Concrete Supply Calculator page is designed for planning quantities rather than structural design. It can tell you the mathematical volume created by your dimensions, but it cannot determine whether a slab should be 100 mm, 125 mm or another thickness. That decision can depend on the use of the slab, soil conditions, reinforcement, loads, engineering details, exposure, drainage, building classification and project approvals. Use the thickness and concrete specification shown on your approved plans, engineering documents or other project requirements where those documents apply.
m³ = Length (m) × Width (m) × Thickness (mm ÷ 1000)For example, if a formed area is 6 m long, 4 m wide and 100 mm thick, the mathematical volume is 6 × 4 × 0.10 = 2.40 m³ before any contingency. The useful part of a calculator is not simply doing that multiplication; it is keeping the base volume separate from any waste allowance so you can see exactly how much extra material is being added.
A generic example cannot account for your actual excavation, access, finished levels, ground conditions or formwork. A slab that looks rectangular on a sketch may contain steps, beams, rebates, thickenings, drainage falls or separate sections. A hand-dug footing can also be wider or deeper than its nominal dimension. Measure the real formed or excavated space as closely as practical before ordering concrete.
For irregular areas, divide the project into simple shapes. Calculate each rectangle or circular section separately and add the volumes. This is usually clearer than trying to force an irregular patio or driveway into one large rectangle. You can also use the Concrete Area Calculator first, then use this page to convert area and thickness into volume.
There is no single waste percentage that is correct for every concrete job. Accurate formwork over a level, well-prepared base may need only a modest contingency, while rough excavation, deep post holes, trenches, thickened edges or multiple small sections can make the required quantity less predictable. The calculator leaves the field at a visual 0 so you decide whether to add 3%, 5%, 10% or another value that reflects your site.
| Thickness | Depth In Metres | Concrete Per 10 m² | Concrete Per 50 m² |
|---|---|---|---|
| 75 mm | 0.075 m | 0.75 m³ | 3.75 m³ |
| 100 mm | 0.100 m | 1.00 m³ | 5.00 m³ |
| 125 mm | 0.125 m | 1.25 m³ | 6.25 m³ |
| 150 mm | 0.150 m | 1.50 m³ | 7.50 m³ |
| 200 mm | 0.200 m | 2.00 m³ | 10.00 m³ |
A circular concrete pad uses the area of a circle. Divide the diameter by two to get the radius, square the radius, multiply by π, then multiply by depth in metres. The calculator performs that calculation automatically. If you have multiple identical pads, enter the number of pads as the quantity. For a circular spa base, tank pad or landscape feature, check that a simple cylinder correctly represents the actual design before using the result as an order quantity.
Volume = π × Radius² × Depth × QuantityFor a straight strip footing, multiply total length by width and depth. The calculator accepts width and depth in millimetres because that is often convenient for site measurements. If the footing changes size along its length, calculate each section independently rather than averaging dimensions. Structural footing dimensions should come from the appropriate plans or engineering information; a volume calculator does not design a footing.
Fence posts, pergola posts and similar holes are commonly treated as cylinders for volume estimating. Enter the hole diameter, depth and number of holes. The optional displacement setting allows a rough reduction for the space occupied by the post itself. For a precise calculation, use the actual cross-sectional dimensions of the post rather than a generic percentage. Our Concrete Fence Post Calculator provides more dedicated post-hole planning.
Bagged concrete can be convenient for small repairs, individual post holes and locations where a concrete truck cannot practically reach the placement area. As volume increases, the bag count can become very large. Instead of assuming that every 20 kg bag makes the same volume, this calculator asks you to enter the manufacturer-stated mixed yield in litres. If a product states a yield of 10 litres, for example, one cubic metre would mathematically require 100 bags before waste because 1 m³ equals 1000 litres. Always use the current data sheet for the actual product you plan to buy.
For larger pours, compare bagged material with a current ready-mix quote. The calculator lets you enter both an A$/m³ ready-mix rate and an A$/bag price. Those figures are intentionally blank on load because product and delivery pricing can change by supplier, suburb, order size, access and service requirements. For another comparison, see the Concrete Bags Per Cubic Yard Calculator.
A concrete cost estimate is only meaningful when the price input matches the quote you are actually considering. A supply-only cubic-metre rate may not include delivery, small-load charges, waiting time, pumping, placement labour, reinforcement, formwork, excavation, base preparation, disposal, sealing or finishing. Enter the concrete rate quoted to you and treat the result as a concrete-material planning figure, not a full installed-project price.
For a broader budget, use the Total Ready-Mix Material Cost Calculator or Ready-Mix Material Cost Calculator alongside supplier and contractor quotes. Keep each cost category separate so you can compare quotes fairly.
A quantity estimate does not determine whether a project needs engineering, certification, permits, inspections or other approvals. Those requirements depend on the type of work, site, building classification and local rules. Use the applicable plans, specifications and advice from the relevant designer, engineer, builder, certifier or authority before concrete is placed.
The calculator should therefore be treated as a materials-planning tool. It can help you quantify a known design, but it should not be used to create the structural design itself.
Outdoor concrete should not be treated as a volume-only problem. Patios, paths and driveways often need controlled falls so water moves toward an appropriate drainage path rather than toward a building or neighbouring property. The correct slope depends on the design and surrounding levels. Use the Concrete Slope Calculator to translate rise and run into percent slope, ratio and angle, but confirm the required drainage design for the site.
An online estimate cannot assign the correct concrete strength, exposure classification, slump, aggregate size or durability requirements. Those choices depend on the project design, environment and applicable standards. Use the concrete specification shown on the relevant plans or obtain appropriate professional advice rather than selecting a mix only because it matches a volume result.
Concrete work can create hazards during mixing, placing, cutting, drilling, grinding and demolition. Concrete and other silica-containing materials can create hazardous dust when cut, drilled, ground or demolished. The safest work method is not determined by this calculator. Follow the current workplace-safety requirements that apply to your location, use appropriate controls and protective equipment, and use qualified trades where required.
| Example Project | Dimensions | Base Volume | Before Waste? |
|---|---|---|---|
| Small pad | 3 m × 3 m × 100 mm | 0.90 m³ | Yes |
| Patio area | 5 m × 4 m × 100 mm | 2.00 m³ | Yes |
| Path | 12 m × 1 m × 100 mm | 1.20 m³ | Yes |
| Thicker slab example | 6 m × 4 m × 125 mm | 3.00 m³ | Yes |
These examples illustrate the mathematics only. They are not recommendations for slab thickness or construction design. Use the required project thickness and specification for your job.
A useful concrete estimate should show more than one final dollar number. Keep the geometric volume, waste allowance, bag yield, ready-mix rate and bag price separate so you can change one assumption without rebuilding the whole calculation. This makes supplier comparisons easier and helps reveal whether a higher total is coming from extra volume, a higher material rate or a different bag yield.
For ready-mix, multiply the waste-adjusted cubic metres by the A$/m³ rate you enter. For bagged concrete, convert the adjusted volume to litres, divide by the mixed yield in litres per 20 kg bag and round up to whole bags. The calculator then multiplies the rounded bag count by your entered bag price. Neither result should be treated as a complete installed-project quote unless all other project costs are deliberately included elsewhere.
| Cost Category | Included Here? | What To Check |
|---|---|---|
| Concrete material | Yes, if you enter a rate | Current supplier A$/m³ or bag price |
| Delivery / short load | Not automatically | Supplier delivery rules and minimum order |
| Pump hire | No | Access, boom/line pump requirement and minimum hire |
| Reinforcement | No | Mesh, bars, chairs and project specification |
| Formwork | No | Timber, stakes, labour and stripping |
| Excavation / base | No | Earthworks, gravel, compaction and disposal |
| Labour / finishing | No | Placement, screeding, finishing, curing and sealing |
A useful concrete supply estimate separates the quantity you physically need from the quantity you may actually order. The base volume comes from project geometry. The waste or contingency percentage increases that volume to cover realistic site variation. A supplier minimum order can then raise the ready-mix order quantity again if your calculated volume falls below the supplier's stated minimum.
This matters because a small slab may mathematically need less than one cubic metre while a local supplier may have a minimum billable load. By keeping the minimum-order field separate, the calculator shows the difference between required concrete volume and orderable supply volume instead of hiding both inside one total.
Supply m³ = Base m³ × (1 + Waste% ÷ 100)If you enter a supplier minimum, the ready-mix order quantity is the greater of the waste-adjusted supply volume and that minimum. The ready-mix material cost is then calculated from the order quantity multiplied by your A$/m³ rate. Any delivery or fixed supply allowance is added after that.
The calculator keeps ready-mix and bagged supply as two separate purchasing paths. Ready-mix pricing uses the orderable cubic-metre quantity. Bagged concrete converts the waste-adjusted volume to litres, divides by the mixed yield per 20 kg bag and rounds up to whole bags. If you enter a bag price, the whole-bag count is multiplied by that price.
A supplier minimum applies only to the ready-mix pathway in this calculator. Bagged concrete is instead constrained by whole-bag rounding. This makes the comparison more realistic for small jobs where buying a few extra bags can be easier than ordering a minimum ready-mix load.
| Supply Component | How It Is Calculated | Included? |
|---|---|---|
| Base concrete volume | Project geometry | Yes |
| Waste / contingency | User-entered percentage | Yes |
| Supplier minimum order | Optional minimum m³ | Optional |
| Ready-mix material cost | Order quantity × A$/m³ | If rate entered |
| 20 kg bag quantity | Adjusted litres ÷ verified L/bag, rounded up | If yield entered |
| Bagged material cost | Whole bags × A$/bag | If bag price entered |
| Delivery / fixed supply cost | User-entered fixed allowance | Optional |
| Pump, labour, reinforcement, excavation | Project-specific | No |
Ready-mix suppliers may price or dispatch concrete subject to minimum quantities, short-load rules or other delivery conditions. If your project needs 0.65 m³ after waste but the supplier minimum is 1.00 m³, entering 1.00 m³ in the minimum-order field makes the ready-mix pricing pathway use 1.00 m³. The base and waste-adjusted project volumes still remain visible so you can see why the billed supply is higher.
Use the delivery or fixed-supply field for a known charge that should be added once to the material estimate. This can represent a quoted delivery fee, short-load allowance, handling charge or another supplier-specific fixed amount. Do not use it for costs that should scale with volume unless you have deliberately converted them to a fixed project allowance.
Use exactly the same project dimensions, thickness, waste allowance and supply volume when comparing quotes. Then change only the supplier rate, minimum order and fixed delivery cost. This produces a like-for-like comparison and makes it easier to see whether a cheaper A$/m³ rate is offset by a higher minimum load or larger fixed charge.
If you are building a larger estimate, combine this page with the Concrete Volume Calculator, Concrete Thickness Calculator, Concrete Coverage Calculator, Concrete Patio Calculator, Concrete Quantity Calculator and Concrete Foundation Calculator. Each tool focuses on a different part of the estimating process, so the underlying measurements should remain consistent between calculators.
Use the calculator result as one input in a broader site and ordering check.
Use the required dimensions, thickness, reinforcement and concrete specification from the appropriate project documents.
Check truck or pump access, placement route, washout arrangements and any supplier delivery requirements.
Check with the relevant certifier or authority whether approvals or inspections apply before concrete is placed.
Quick answers about volume, bags, waste, pricing and local project planning.
It estimates the project volume, adds any waste allowance, converts the result to an orderable ready-mix quantity or whole 20 kg bags, and can calculate material and delivery costs from the rates you enter.
Yes. Enter the supplier minimum in cubic metres. If your calculated ready-mix supply volume is lower, the pricing pathway uses the minimum order quantity.
No. The base and waste-adjusted project volumes remain unchanged. The minimum only affects the ready-mix order quantity and related supply cost.
Yes. Enter it in the Delivery / Fixed Supply Cost field. It is added once to both supply-cost pathways when those pathways have enough information to calculate a total.
No. It is focused on concrete supply. Pumping, labour, reinforcement, excavation, formwork and finishing should be added separately unless you intentionally include them in another project budget.
Multiply length in metres by width in metres by depth in metres. If the thickness is in millimetres, divide it by 1000 first.
The visible 0 is a placeholder only. The real field is empty, so when you type 5 you get 5 rather than 05. Reset returns the field to that empty placeholder state.
Only if you enter a waste percentage. The base volume and volume-with-waste are shown separately so you can see the effect of the allowance.
There is no universal percentage. The appropriate contingency depends on measurement accuracy, excavation, formwork, thickenings and site conditions. Re-measure before ordering.
Yes, if the patio can be represented by the available shapes and you know the required thickness. For more patio-specific inputs, use the Concrete Patio Calculator.
You can use it to estimate geometric concrete volume from known dimensions. It does not determine driveway thickness, reinforcement, crossover requirements, drainage or approvals.
Divide 1000 litres by the manufacturer-stated mixed yield per bag, then round up to whole bags. Different products can have different yields.
Only to the extent that the rate you enter includes delivery. Use the exact basis of your supplier quote and keep other costs separate.
No. Use the strength and specification required by the engineer, plans, builder, certifier or other applicable project documents.
Yes. Select Round Pad and enter diameter, depth and quantity.
Yes. Enter the total footing length, width and depth. The tool calculates volume only and does not design the footing.
Yes. Select Post Holes and enter hole diameter, depth and quantity. A dedicated fence-post calculator is also internally linked for more detailed planning.
Yes. Use the slab option when the pour can be represented by length, width and thickness. For irregular work, calculate separate simple sections and combine the volumes. The calculator estimates quantity only; it does not choose the structural thickness, reinforcement, drainage falls or concrete specification.
No. Approval, engineering and inspection requirements depend on the project and location. Check the applicable plans, certifier, engineer and local authority requirements separately.
Concrete and delivery costs can change by supplier, order size, location, access and service requirements. A current quote is more useful than a fixed online price.
No. It is a quantity and cost-planning tool only. Structural dimensions, reinforcement, strength, exposure requirements and approvals must come from the appropriate project information and professionals.
Use technical guidance, the project specification and current supplier information alongside any online concrete estimate.
Australian industry guides covering concrete construction, residential slabs, placing and related technical topics.
View CCAA Technical GuidesUse the dimensions, thickness, reinforcement, strength and detailing shown on the approved project documents where they apply.
Review The Estimating GuideConfirm current A$/m³ pricing, minimum loads, delivery fees, waiting time, access, pumping and order increments directly with the supplier.
Update Your Cost InputsCross-check volume, thickness, coverage, foundations, post holes and total concrete cost with related estimating tools.
Open Concrete Volume Calculator