Slab
Calculate a rectangular slab from its finished dimensions.
- Volume = length × width × depth. Bag yield is cured volume from the product label, not bag mass. This is quantity planning, not structural design.
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Concrete Calculator
Calculate slab or cylinder volume and convert it into bags using the actual product yield.
What does a worked calculation look like?
A 5 × 4 m slab at 10 cm deep holds 2 m³ of concrete, or 2.2 m³ with a 10% allowance. That is 2,200 L; bags that yield 12 L each mean 184 bags. At this size, ready-mixed delivery is usually more practical than bags.
Method and practical checks
- Volume = length × width × depth. Bag yield is cured volume from the product label, not bag mass. This is quantity planning, not structural design.
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Every calculation option
Round volume
Use for cylindrical quantities with a measured diameter.
- Cylinder volume = π × radius² × height × count. Structural dimensions must come from a suitable design.
Known volume to bags
Enter a volume from another measurement or supplier estimate.
- Apply the allowance once. Round bags up only after converting the final required volume to litres.
Worked example
A 5 × 4 m slab at 10 cm deep holds 2 m³ of concrete, or 2.2 m³ with a 10% allowance. That is 2,200 L; bags that yield 12 L each mean 184 bags. At this size, ready-mixed delivery is usually more practical than bags.
| Input | Value |
|---|---|
| Length | 5 m |
| Width | 4 m |
| Depth | 10 cm |
| Extra allowance | 10 % |
| Yield per bag | 12 L |
| Result | Value |
|---|---|
| Volume before allowance | 2 m³ |
| Concrete volume | 2.2 m³ |
| Required quantity | 2,200 L |
| Packs to buy | 184 |
| Purchase quantity | 2,208 L |
| Left over | 8 L |
Reading the result
- Bag yield is the cured volume stated on the bag, not its weight. Check your product; yields differ between mixes.
- This is a quantity estimate only. Slab thickness, reinforcement and sub-base depend on the load and ground, and need appropriate design advice.
- Uneven excavation is the usual reason for running short; the allowance covers it only if the base is reasonably level.
Which unit should the slab depth use?
Keep every dimension in the units shown by the selected mode. Length × width × depth gives volume only after the dimensions are compatible. A 3 × 2 m slab 0.1 m deep is 0.6 m³ before allowance; entering 10 as metres would be a major error.
Can I turn concrete volume directly into a bag weight?
Use the chosen product's stated yield per bag. Bag weight alone does not establish mixed volume. The calculator's yield is an editable purchasing input, and the calculation does not design a structural slab or approve its reinforcement, ground preparation or curing method.
How does the slab-volume example work?
A rectangular slab 4 m long, 3 m wide and 0.1 m deep contains 1.2 m³ before allowance: multiply the three dimensions in metres. An entered allowance changes the order volume separately. This quantity calculation does not establish reinforcement, structural suitability or a concrete mix; use the project's specifications.
Calculation/content reviewed 4 October 2026. Source: Babushka Market’s displayed formulas, units and labelled editable assumptions. How the estimates work