How to Calculate Concrete Volume
A practical guide to calculating concrete quantities for slabs, footings, walls, columns and circular forms, with formulas you can verify by hand.
Start with the shape
The correct concrete formula depends on the geometry. Convert all dimensions into one unit system before multiplying. For rectangular elements such as slabs, pads, footings and walls, use length × width × depth. For round elements, calculate the circular area first.
Concrete Slab Example
Suppose a slab is 20 ft long, 30 ft wide and 4 in thick.
Convert 4 inches to feet: 4 ÷ 12 = 0.333333 ft.
Volume = 20 × 30 × 0.333333 = 200 ft³.
Since 27 ft³ = 1 yd³, the volume is 200 ÷ 27 = 7.407407 yd³.
The same volume is about 5.663369 m³.
Concrete Footing Calculation
For a rectangular footing, use the same rectangular-volume formula. For example, a footing 2 m long, 0.6 m wide and 0.3 m deep has:
If there are 8 identical footings, multiply by quantity:
Round Column or Circular Footing
Use the circle area formula followed by height. A round element 0.4 m in diameter and 2 m high has:
For several identical columns, multiply that volume by the quantity.
Add a Waste Allowance Separately
Waste should be applied after the geometric volume is correct:
For example, 5.00 m³ with a 10% allowance becomes 5.50 m³. The appropriate allowance depends on measurement accuracy, placement conditions and supplier practice; 10% is not a universal requirement.
How to Convert Concrete Volume
ToolVault uses exact conversion constants internally and rounds only displayed values.
Volume Is Different from Concrete Mix Design
Calculating how much concrete you need does not determine the correct cement, aggregate and water proportions or structural strength. Mix design, reinforcement, specifications and code requirements are separate engineering decisions.
Common Concrete Calculation Mistakes
- Mixing metres, centimetres, feet and inches without converting them first.
- Using a fixed number of bags for every concrete product.
- Applying waste before calculating the actual geometric volume.
- Assuming concrete density is identical for every mix.
- Treating a quantity calculation as a structural design approval.
Use the Free Concrete Calculator
ToolVault's Concrete Calculator automates these formulas for multiple elements and supports metric and imperial measurements, waste allowance, weight, cubic yards, cubic feet and manufacturer-based bag yields.
Calculate your concrete quantity
Enter your actual dimensions and let the calculator handle the geometry and unit conversions.
Open Concrete Calculator →