Material calculator
Concrete Slab Calculator
Enter the dimensions of each rectangular pour to estimate concrete volume.
Your measurements
Changing units changes the display, not the stored measurement.
Results
Example inputs
Your result will appear here
Enter the measurements and product details, then calculate.
These tools estimate material quantities from dimensions you choose. They do not specify structural depth or load capacity.
Measure the space to be filled
Enter the length, width and depth of the concrete volume. Use the dimensions specified for your project rather than taking an example thickness as a recommendation. Where the shape changes, record another non-overlapping rectangle. A section counted twice will also be counted twice in the total.
Keep the units visible. A depth entered in millimetres must be converted to the same length basis as the plan dimensions before multiplication. Switching display units should describe the same physical space, not create a new measurement.
Read the volume in layers
The net quantity is the sum of the included rectangular slab volumes. Leave unfilled parts out by dividing the pour into non-overlapping rectangles; this form has no separate volume-deduction field. Your selected allowance is applied once to the net quantity. If you need bags, the next step uses the mixed yield of the particular product you choose.
Example: one small rectangular slab
For an illustrative 3 m by 2 m area with a user-selected depth of 0.1 m, the net volume is 0.6 m³. A chosen 10% allowance adds 0.06 m³, giving a required volume of 0.66 m³. These are arithmetic inputs, not a recommended patio specification.
If another section has a net volume of 0.2 m³, the combined net volume is 0.8 m³. Applying the same 10% allowance once gives 0.88 m³. Do not add a second allowance after combining the results.
Check before converting to bags
Record the required volume in your project, then enter a product yield if you want a bag count. Bag mass is not the same as mixed volume. Confirm the yield and purchasing unit from the product information.
What this estimate covers
The tool calculates geometric quantity. It does not choose depth, reinforcement, concrete strength, sub-base preparation or structural suitability. Uneven levels or a non-rectangular shape need measurements that represent the actual volume.
Frequently asked questions
Can I add more than one slab?
Yes. Keep each rectangle separate and avoid overlap. Compatible material requirements can be combined before purchasing, with the allowance applied only once to each measured quantity.
Why is the bag count a separate step?
The slab dimensions determine a volume. A bag count also needs the mixed yield of the product you intend to buy.
Sources and method
- PackLedge quantity methods
Original derivations using geometry, ratios, sums and whole-package rounding. Each calculator explains its assumptions and worked examples.
- NIST Guide to the SI — Conversion Factors ↗
Reference for unit conversions and clear identification of metric and customary units. Exact base-unit definitions are retained in calculations rather than rounded display factors.