Estimate Wet Concrete Volume And A Planning Quantity Of Cement, Sand And Aggregate For A Rectangular Concrete Slab. Enter Your Slab Dimensions, Choose A Nominal Mix Ratio, Add Waste, Then Compare Material Quantities And Cost.
All Fields Start Blank With A Soft Zero Placeholder. Type Your Own Measurements And The Zero Will Not Be Added In Front Of The Number. Choose A Preset Nominal Ratio Or Enter Your Own Cement : Sand : Aggregate Parts; Results Stay Hidden Until You Press Calculate Slab Materials.
Enter Relative Parts Only. For Example, 1 : 2 : 3 Means 1 Part Cement, 2 Parts Sand And 3 Parts Coarse Aggregate.
Press Calculate Slab Materials To See The Result.
First Calculate The Finished Slab Volume. Then Add Your Waste Allowance. For Site-Mix Planning, Convert That Wet Volume To A Larger Loose Dry-Material Volume And Split It By The Selected Cement : Sand : Aggregate Ratio.
Move From Basic Slab Geometry To A Transparent Material Breakdown Without Hiding The Planning Assumptions.
Finished slab volume from length, width, thickness and quantity.
Approximate whole bags from cement share, density basis and bag size.
Loose fine-aggregate planning volume from the selected mix ratio.
Loose coarse-aggregate planning volume from the selected mix ratio.
Add your own percentage for real site variation and handling.
Use your own bag and bulk-material rates instead of fixed prices.
Measure The Slab First, Then Separate Geometry From Material-Mix Assumptions.
A concrete slab material calculation begins with the finished concrete shape. Measure the slab length and width in metres and enter the designed slab thickness in millimetres. The calculator converts thickness to metres before multiplying the three dimensions. If several slabs are identical, use the quantity field; if they are different sizes, calculate each slab separately and add the results.
For a thickness entered in millimetres, divide by 1,000 before multiplying.
Finished concrete is a compacted composite material. Loose cement, sand and coarse aggregate contain voids before mixing and consolidation. A site-mix material estimate therefore uses a dry-volume factor that is larger than the finished wet-concrete volume. This page lets you choose a planning factor instead of hiding that assumption. The default select option is 1.54, while alternative planning factors are available for comparison.
The Cement Concrete & Aggregates Australia guide describes concrete in its basic form as a mixture of cement, water, fine aggregate and coarse aggregate, and emphasises that quality concrete depends on materials, proportions, production, placing and curing. A simple volume ratio is therefore useful for estimating loose materials, but it is not a complete performance specification.
The preset ratios are included to help with quantity planning when a nominal proportion has already been chosen for a non-critical use or preliminary estimate. They are not recommendations for slab strength. A structural slab, driveway, industrial floor, suspended slab, footing-integrated slab or other engineered work may require a specified concrete strength and a designed mix supplied by a batch plant or prepared under a qualified specification.
The calculator supports 1:2:3, 1:1.5:3 and 1:3:6 planning ratios plus a custom mode. In each ratio, the first part is cement, the second is sand and the third is coarse aggregate. The program totals the parts and assigns the selected share of the dry material volume to each constituent.
Cement is first estimated as a loose volume share. That volume is converted to kilograms using the selected bulk-density planning basis, then divided by the selected bag size and rounded up to whole bags. Bulk density can vary with product and handling, so a bag count derived this way is a planning estimate rather than a product-specific batching instruction. When exact batching matters, use the product data, batch weights or an approved mix design.
Sand and aggregate results are shown as approximate loose volumes. Moisture, grading, compaction, stockpile condition, bulking and supplier measurement methods can change the amount delivered or weighed. If your supplier sells by tonne rather than cubic metre, use the supplier's current bulk-density information to convert volume to mass instead of assuming one density for every material.
The mathematical slab volume assumes perfect dimensions. Real sites can have low spots, uneven subgrade, form movement, small over-excavations and handling losses. The waste field lets you add a percentage that suits the actual job. Keep the field at zero if you only want the geometric volume, then compare an allowance separately before buying materials.
No extra rounding is applied by default. If you select 0.05 m³ or 0.10 m³, the wet volume after waste is rounded upward before the dry material estimate is calculated. This keeps the material split tied to the displayed final wet-volume planning target.
Enter your own cement bag price plus sand and aggregate rates per cubic metre. The calculator multiplies each material quantity by its entered rate. Water, admixtures, reinforcement, vapour barriers, subbase, formwork, labour, equipment, pumping, finishing, curing, delivery and disposal are not included in this material-only cost unless you add them separately.
The Result Is Most Useful When You Know What Each Quantity Represents And What It Leaves Out.
Cement and concrete are not interchangeable terms. Cement is the powder binder that reacts with water; concrete is the finished composite made with cementitious material, water and aggregates. Buying enough cement bags alone does not establish that a mix will achieve the required strength, workability, durability or shrinkage performance.
Fine aggregate is commonly sand or a manufactured fine aggregate meeting the relevant product and project requirements. Its grading and moisture condition influence water demand, workability and batching. For a preliminary volume estimate, the calculator assigns sand according to the ratio you selected.
Coarse aggregate forms a major portion of concrete volume. Aggregate size, grading, shape, cleanliness and source all affect concrete behaviour. The calculator uses a simple ratio share and does not assess whether a particular aggregate is suitable for the slab thickness, reinforcement spacing, finish or exposure conditions.
This calculator deliberately does not invent a water quantity. Water demand is not safely derived from a generic cement:sand:aggregate volume ratio alone. The required water-cement ratio, aggregate moisture corrections, admixtures and target workability belong to the actual mix design, product instructions or supplier specification.
Mesh, reinforcing bars, chairs, laps, edge thickenings, beams and local strengthening are not material outputs here. For reinforcement planning, use a dedicated reinforcement tool or the project drawings. For a thicker edge beam or integrated footing, calculate that additional concrete geometry separately.
For larger slabs, ready-mixed concrete is often ordered by cubic metre, while small repairs and minor slabs may use bagged or site-batched materials. This calculator is most useful when you specifically want a constituent-material estimate. If you only need the concrete order volume, use the Concrete Volume Calculator or Concrete Quantity Calculator. For broader pricing, compare the Total Concrete Cost Calculator.
These Examples Demonstrate Quantity Arithmetic Only. They Do Not Specify A Suitable Concrete Mix For A Particular Structure.
| Example Slab | Dimensions | Wet Volume | Planning Ratio | Dry Factor | Purpose Of Example |
|---|---|---|---|---|---|
| Small Pad | 2 m × 2 m × 100 mm | 0.40 m³ | 1 : 2 : 3 | 1.54 | Shows basic slab geometry and constituent split. |
| Shed Slab | 4 m × 3 m × 100 mm | 1.20 m³ | 1 : 2 : 3 | 1.54 | Shows how area and thickness scale material demand. |
| Larger Slab | 6 m × 5 m × 120 mm | 3.60 m³ | Custom | User Selected | Demonstrates why specified mixes should be checked before bulk buying. |
Measure the formed slab and any beams or thickened edges separately.
Check required grade, strength, exposure, slump and supplier instructions.
Confirm whether sand and aggregate are sold by volume, mass or load.
Plan mixing, delivery, pumping, barrow access and uninterrupted placement.
Keep reinforcement, finishing and curing requirements separate from mix quantity.
Compare the calculator result with project documents and current supplier data.
Multiply slab length by width by thickness after converting thickness to metres. Multiply by the number of identical slabs if required.
It estimates finished concrete volume plus approximate cement, sand and coarse aggregate quantities for a selected nominal volume ratio.
Yes. On this page the ratio order is cement : sand : coarse aggregate.
Loose dry constituents contain voids before mixing and consolidation. A planning dry-volume factor is used to convert finished concrete volume to approximate loose constituent volume.
No. It does not invent a water quantity because water demand and water-cement ratio depend on the actual mix design, aggregate moisture, admixtures and specification.
The cement share is converted from volume to approximate mass using the selected density basis, divided by the selected bag size and rounded up to whole bags.
Yes. Select Custom Mix and enter your cement, sand and aggregate parts.
No. It only uses the cement bag, sand and aggregate rates you enter.
Zero provides a clear reset state. When you focus a zero field it clears so your typed number replaces the zero rather than being added after it.
No. Use the required project concrete grade and mix design. This tool is for quantity planning only.
Australian technical guide covering concrete constituents, production, properties, construction and related practice.
Open CCAA GuideOverview explaining the relationship between cement, water, sand, gravel and finished concrete.
Open Concrete OverviewNational work-health-and-safety information on concrete pumping hazards and risk controls.
Open Safe Work AustraliaCross-check slab volume, concrete quantity and overall cost using related calculators.
Open Concrete Volume Calculator