The formula
Volume (m³) = length (m) × width (m) × depth (mm) ÷ 1,000. Add your chosen allowance. Bags = volume (litres) ÷ yield per bag, rounded up.
Building • UK CALCULATOR
Concrete Calculator UK
Estimate how much concrete you need for a rectangular slab, shed base or simple pad. See the finished volume and the number of pre-mixed bags you may need.
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Your estimate starts here
Enter your measurements and calculate to see materials, quantities and an optional price estimate.
GOOD TO KNOW
How this calculator works
Worked example
A 3 m × 2 m slab at 100 mm deep needs 0.60 m³ before wastage. At 10% extra, that becomes 0.66 m³.
Check before ordering
Bag yield differs by product, water addition and compaction. The default 11.5 litres per 25 kg bag is illustrative: use your bag label. A concrete calculator does not determine slab thickness, reinforcement or suitability for loads.