Wall volume formula
V = L(ft) × H(ft) × T(in) ÷ 12
yd³ = V ÷ 27
battered (sloped) wall: V = L × ((top T + bottom T) ÷ 2) × H
For a wall that is thicker at the base, pick the trapezoid shape and enter the top and bottom widths. The average width times the height gives the cross-section.
Worked example: 20 ft wall, 4 ft tall, 8 in thick
- Thickness in feet: 8 ÷ 12 = 0.667 ft.
- Volume: 20 × 4 × 0.667 = 53.33 ft³.
- Cubic yards: 53.33 ÷ 27 = 1.98 yd³.
- 80 lb bags: 53.33 ÷ 0.60 = 88.9, so 89 bags. A truck is likely easier here.
Walls with several runs
A foundation is often four walls of different lengths. Add each as a section. At corners, avoid double counting. Use outside lengths on two opposite walls and inside lengths on the other two.
Footings, block, and forms
- The footing under the wall is separate. Use the concrete footing calculator, or combine both in the main concrete calculator.
- Building with CMU instead of poured concrete? The concrete block calculator counts blocks and core fill.
- Form walls can bulge slightly under the weight of wet concrete. A few percent of waste covers that.
Volume only. Wall thickness, height limits, and reinforcement, especially for retaining walls, come from your plans or an engineer.