Concrete Wall Calculator
Enter the length, height and thickness of your wall and this concrete wall calculator returns the volume in cubic yards and cubic meters, bag counts and a cost estimate. It handles poured foundation walls, stem walls and retaining walls, and it subtracts door and window openings.
Concrete Wall Calculator
A poured wall is a tall, thin slab, so the math is the same length times height times thickness. The part people forget is the openings. Subtracting a doorway or a window keeps you from ordering concrete you will never place.
How to calculate concrete for a wall
Volume equals length times height times thickness, all in the same unit, with the area of any openings removed before you multiply by thickness. Divide the cubic feet by 27 for cubic yards.
Worked example, a foundation wall
Take a wall 20 feet long and 8 feet tall at 8 inches thick, with one 3 by 7 foot doorway. The face area is 20 times 8, or 160 square feet. The door removes 21 square feet, leaving 139. Convert the thickness: 8 divided by 12 is 0.667 feet. Multiply: 139 times 0.667 is about 92.7 cubic feet, which is 3.43 cubic yards. Add 10 percent for waste and order about 3.8 yards. A wall this size is a ready mix pour, since it is near 155 bags.
Wall thickness and reinforcement
| Wall type | Typical thickness | Notes |
|---|---|---|
| Foundation or stem wall | 8 to 10 in | Below grade, carries the structure above |
| Garage or basement wall | 8 in | Common residential pour |
| Retaining wall | 8 to 12 in | Resists soil pressure from one side |
Poured walls use vertical and horizontal rebar sized to the load and the wall height. Keep cover between the steel and the form, and tie the wall steel into the footing below so the two act together. Reinforcement controls how the wall resists bending; it does not change the concrete volume.
Retaining walls need extra care
A retaining wall holds back soil, so it carries side pressure that a plain wall does not. Short garden walls under about 4 feet are often built without an engineer, but taller walls, walls holding a slope, or walls with a surcharge such as a driveway above usually require an engineered design. The International Building Code and local rules set the threshold. A retaining wall also needs drainage behind it, since trapped water adds pressure that can push the wall over.
Related calculators
- Footing calculator for the footing under the wall
- Concrete block calculator if you are building with block instead of a poured wall
- Bags calculator to total bags for a short wall
- How to calculate concrete guide for formulas
Frequently asked questions
How much concrete do I need for a wall?
Multiply length by height, subtract any openings, then multiply by thickness and divide by 27 for cubic yards. A 20 by 8 foot wall at 8 inches with one door needs about 3.43 cubic yards.
How thick should a concrete wall be?
Residential foundation and basement walls are usually 8 inches. Retaining walls run 8 to 12 inches depending on height and soil load.
Do concrete walls need rebar?
Yes. Poured walls use vertical and horizontal bars tied into the footing. Size and spacing follow the structural drawings and local code.
When does a retaining wall need an engineer?
Walls over about 4 feet, walls holding a slope, or walls with load above them usually need an engineered design and a permit. Check your local code.
Does a retaining wall need drainage?
Yes. Gravel backfill and a drain behind the wall relieve water pressure, which is a leading cause of retaining wall failure.
References
- International Building Code and ICC resources on retaining walls: https://codes.iccsafe.org
- American Concrete Institute, ACI 318: https://www.concrete.org
- Quikrete, Concrete Mix 1101 data sheet (bag yields): https://www.quikrete.com/PDFs/DATA_SHEET-Concrete Mix 1101.pdf
- Portland Cement Association, concrete technology library: https://cement.org
Methodology: volume uses length times height minus openings, times thickness, divided by 27 for cubic yards; bag counts use published yields. Estimates are for planning. Confirm wall thickness, reinforcement and retaining wall design with a licensed engineer and local code. Recommended: attribute this page to a named author and add a review date.