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Wall Concrete Calculator
Estimate concrete for retaining and garden walls. Enter length, height and thickness: get cubic yards and bags instantly.
Estimates only. Bag yields per manufacturer specs (80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³). Ready-mix trucks carry ≈ 10 yd³. Always round up and confirm with your supplier.
Retaining walls, garden walls and foundation walls all start with an accurate volume. The free wall concrete calculator below turns length, height and thickness into cubic yards, bag counts and cost, so you order neither too little nor too much.
How to use the wall concrete calculator
- Measure the wall length in feet.
- Enter the wall height in feet, from footing to top.
- Enter the wall thickness in inches (8 inches is standard for block-filled or poured walls).
- Add 10 percent waste for formwork gaps and spillage.
Formula
Volume = Length × Height × (Thickness ÷ 12) ÷ 27, giving cubic yards.
Practical tips
- An 8 inch thick wall, 20 ft long and 4 ft high needs 2.37 cubic yards.
- Retaining walls over 3 ft high usually need drainage behind them and an engineer check.
- Pour walls in one go where possible to avoid weak cold joints.
- Vibrate or rod the concrete in the forms to remove air pockets.
Frequently asked questions
How thick should a concrete retaining wall be?
Eight inches is the minimum for most garden retaining walls. Taller walls need thicker sections or reinforcement.
How much concrete for a 20 ft wall?
A 20 ft long, 4 ft high, 8 in thick wall needs about 2.4 cubic yards (107 bags of 80 lb mix).
Do I need drainage behind a retaining wall?
Yes. Water pressure is the top cause of wall failure. Add gravel backfill and a drain pipe.
Explore the full concrete calculator or price the job with the cost estimator.
Worked examples
Example 1: 20 ft wall, 8 ft high, 8 in thick. Volume = 20 x 8 x (8 / 12) / 27 = 3.95 cubic yards. With 10% waste: 4.35 cubic yards (196 x 80 lb bags).
Example 2: 30 ft wall, 8 ft high, 8 in thick. Volume = 5.93 cubic yards. With 10% waste: 6.52 cubic yards (294 x 80 lb bags).
Wall concrete reference table
Cubic yards before waste; 80 lb bags include 10% waste.
| Wall size | Cubic yards | 80 lb bags |
|---|---|---|
| 20 x 8 ft, 8 in thick | 3.95 | 196 |
| 20 x 8 ft, 6 in thick | 2.96 | 147 |
| 30 x 8 ft, 8 in thick | 5.93 | 294 |
| 20 x 4 ft, 8 in thick | 1.98 | 98 |
More wall questions
How thick should a concrete wall be?
Basement and retaining walls are commonly 8 inches thick. Structural walls need proper reinforcement, so follow an engineer’s design.
Does the calculator include the footing?
No. This tool calculates the wall only. Estimate the footing separately and add the two volumes.
How many bags for an 8 inch wall?
A 20 ft long, 8 ft high, 8 in thick wall needs 196 x 80 lb bags with 10% waste.