Measure finished depth
Volume is length × width × depth, with all three lengths in consistent units. Metric depth inputs use millimetres. Imperial depth uses inches, while surface lengths use feet.
06 / Patios & paths
Concrete slab calculator
Calculate mixed concrete volume for rectangular sections and estimate bags using the mixed yield stated on your product.
Know what goes into your estimate
Match the volume to the mix
Bag weight and mixed yield are different measurements.
Read the mixed yield
Use the volume one bag produces after mixing, as specified by its manufacturer. Do not enter the bag’s weight as litres. Different products and bag sizes can have different yields.
Choose bags or bulk
Add your allowance, then divide by bag yield and round up. For bulk, the minimum displayed amount rounds upward to 0.001 m³ or yd³; suppliers may require much larger increments.
Concrete volume for a 3 × 2 m section
Depths are calculation examples, not suitable-thickness recommendations. Each bag is assumed to produce 10 L after mixing; dry bag weight cannot replace mixed yield. Use your specified depth and the selected mix’s actual yield.
| Entered depth | Geometric volume | With 10% extra | Bags at 10 L yield |
|---|---|---|---|
| 50 mm | 0.3 m³ | 0.33 m³ | 33 |
| 100 mm | 0.6 m³ | 0.66 m³ | 66 |
| 150 mm | 0.9 m³ | 0.99 m³ | 99 |
| 200 mm | 1.2 m³ | 1.32 m³ | 132 |
These are examples, not product specifications. Enter your own measurements and product details in the calculator above.
Common questions
How much concrete fills a 3 × 2 m section at 100 mm?
The geometric volume is 3 × 2 × 0.1 = 0.6 m³, or 600 L. With 10% extra, it becomes 660 L. If the selected bag makes 10 L of mixed concrete, that is 66 bags. The 100 mm depth and 10 L yield are example inputs, not specifications.
Why is there a mixed-yield input instead of bag weight?
A 20 kg label describes dry mass, not mixed volume. Use the manufacturer’s stated yield. The calculator avoids assuming that all bags with the same weight produce the same volume.
Does this choose a suitable slab thickness?
No. Enter the depth specified for your project. Loads, soil, reinforcement, drainage and local requirements can affect the design; quantity arithmetic cannot assess those conditions.
Can I calculate curved areas or post holes?
This version supports rectangular sections only. Do not use the rectangle’s bounding area for a circle. Post displacement and cylindrical holes are not calculated here.
Where can I check product-specific quantities?
QUIKRETE’s official calculator provides estimates for its own mixes and bag sizes. Compare your result against the selected product’s published yield and instructions.