Concrete Bag Calculator: measuring notes and method
Read finished yield, not bag weight
Bag mass and finished volume are different quantities: a 20 kg bag does not mean 20 L of mixed concrete. For 0.3 m³ at a 12 L yield, 300 ÷ 12 gives 25 bags before allowance.
Decide where allowance is applied
When transferring an order volume from the slab tool, use zero additional waste here if that volume already includes it. Round the final bag count up once and check the purchased yield against the required volume.
CHECK A PRACTICAL EXAMPLE
Same pour, different mixed yield
Both estimates start with 0.3 m³ and no extra allowance. The yields are illustrative label values.
12 L per bag
- Bags to buy
- 25
- Volume including waste
- 0.3 m³
13 L per bag
- Bags to buy
- 24
- Volume including waste
- 0.3 m³
Compare the finished yield printed on the actual bags. A smaller bag count does not by itself mean a lower cost; multiply each whole-bag count by that product’s price.
Fixed comparison in metric units. Values are illustrative unless linked to a recorded project; changing the calculator above does not change this example.
Formula
Bags = round up [volume × (1 + waste ÷ 100) ÷ mixed yield per bag].
Product reference: QUIKRETE product yields
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Required concrete volume
- 0.5 m³
- Mixed yield per bag
- 12 L
- Waste allowance
- 10 %
Bags to buy: 46
Imperial worked example
- Required concrete volume
- 0.654 yd³
- Mixed yield per bag
- 0.4238 ft³
- Waste allowance
- 10 %
Bags to buy: 46
Follow the calculation
- Allowance multiplier = 1 + 10 ÷ 100 = 1.1.
- Required volume = 0.5 × 1.1 = 0.55 m³.
- Bag yield = 12 L = 0.012 m³. Divide required volume by 0.012 and round up to whole bags.
Unit conversions
1 m³ = 1,000 L ≈ 1.30795 yd³. One cubic yard is 27 ft³.
Reviewed 19 October 2026. How calculations are checked · Report a correction