How much concrete for a 20 ft wall?
A 20 ft long × 8 ft high × 8 in thick wall needs 106.7 cubic feet, or 3.95 cubic yards, before waste. Add 10% for about 4.35 cubic yards.
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Concrete Wall Calculator
Estimate the concrete needed for a poured wall, stem wall or retaining wall. Enter the wall length, height and thickness to get volume, bags, rebar and cost.
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How to calculate concrete for a wall
Wall volume = length × height × thickness. Convert the thickness from inches to feet by dividing by 12, then divide the cubic feet by 27 for cubic yards.
Example: 20 ft long × 8 ft high × 8 in thick
20 × 8 × (8 ÷ 12) = 106.7 cubic feet. Divide by 27 to get 3.95 cubic yards. Add 10% waste for about 4.35 cubic yards, or roughly 204 × 80 lb bags. Ready-mix is usually the practical choice at this size.
Common wall sizes
| Size | Concrete | 80 lb bags* |
|---|---|---|
| 10 ft × 4 ft × 6 in | 0.74 cu yd | 35 |
| 20 ft × 4 ft × 6 in | 1.48 cu yd | 70 |
| 20 ft × 8 ft × 8 in | 3.95 cu yd | 185 |
| 30 ft × 6 ft × 8 in | 4.44 cu yd | 208 |
*Before waste. Add 5–10% for spillage and uneven subgrade.
Tips for ordering concrete for a wall
- Add 5–10% waste for spillage and uneven formwork.
- Use 6–8 in thickness for many residential stem walls; retaining walls need an engineered design.
- Order ready-mix for walls above about 1 cubic yard; bagging large walls is slow and costly.
- Confirm rebar size, spacing, cover and wall drainage with your engineer or building plan.
Concrete Wall Calculator FAQ
How thick should a concrete wall be?
Residential stem walls are often 6–8 in thick. Retaining walls and load-bearing walls need an engineered thickness based on height, soil and loads. Do not size a structural wall by rule of thumb alone.
How many bags of concrete for a wall?
A 20 ft × 8 ft × 8 in wall needs about 185 × 80 lb bags before waste, or roughly 204 bags with 10% waste. At that scale, ready-mix is usually cheaper and faster.
Do concrete walls need rebar?
Most structural and retaining walls use horizontal and vertical rebar. The size, spacing and cover depend on the design; follow the engineered plan or local code.
How do I calculate a retaining wall?
Use the wall length, height and thickness in the calculator. Retaining walls also need a footing, drainage and an engineered design; the concrete volume is only one part of the estimate.
How much does a concrete wall cost?
At $120–$180 per cubic yard, 4.35 cubic yards of ready-mix costs about $520–$780 before delivery. Formwork, reinforcement, excavation and finishing are separate costs.
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