How the calculation works
First calculate the concrete volume. Then increase it by the selected allowance and divide by the bag's stated yield. The result is rounded up to a whole bag.
Worked example
A 3 m × 2 m slab at 10 cm thickness is 0.6 m³. With 10% allowance and a bag yield of 0.02 m³, the estimate is 33 bags.
Product note: Bag yield varies by product. Always use the yield printed on the actual bag or technical sheet, and follow the manufacturer's mixing instructions.
Common mistakes
- Using bag weight instead of bag yield.
- Forgetting that 10 cm is 0.10 m.
- Rounding down the final bag count.
FAQ
Should I buy an extra bag?
For a small pour, an additional bag can be practical if the supplier allows it, but the right allowance depends on site conditions and the product.