Concrete Wall Calculator
Short answer: a 20 ft long, 8 ft high wall at 8 inches thick needs 3.95 cubic yards (4.35 with 10% waste) — about 196 × 80 lb bags. Enter your wall below.
Calculate your wall
How the calculation works
Gross volume = length × height × thickness, all in feet (thickness in inches ÷ 12). Openings = opening area × thickness. Net volume = gross volume − openings, then ÷ 27 for cubic yards, plus your waste allowance.
Worked example: a 20 × 8 ft wall at 8 in thick, no openings: 20 × 8 × (8 ÷ 12) = 106.67 cu ft = 3.95 cubic yards. With 10% waste: 4.35 cubic yards, or about 196 × 80 lb bags. A 21 sq ft door opening in the same wall would leave 3.43 cubic yards net.
Common poured walls at 8 inches thick (before waste)
| Wall | Concrete (net) | 80 lb bags (net) |
|---|---|---|
| 10 ft × 4 ft | 0.99 cubic yards | 45 |
| 20 ft × 4 ft | 1.98 cubic yards | 89 |
| 20 ft × 8 ft | 3.95 cubic yards | 178 |
| 30 ft × 8 ft | 5.93 cubic yards | 267 |
| 40 ft × 8 ft | 7.90 cubic yards | 356 |
Volumes are net (before waste, no openings). Bag counts use the 0.60 cu ft yield and are rounded up.
Frequently asked questions
How much concrete do I need for a 20x8 foot wall?
At 8 inches thick with no openings: 3.95 cubic yards net, 4.35 with 10% waste — about 196 × 80 lb bags.
How do you calculate concrete for a wall?
Length × height × thickness, minus opening area × thickness, all in feet — then divide by 27 and add waste.
How thick should a poured concrete wall be?
8 inches is common for residential foundation walls, but thickness, reinforcement and footing size are set by the design and local code, not by this calculator.