Retaining Wall Cost Calculator - Materials & Cost Estimate

What is a retaining wall cost calculator?

A retaining wall cost calculator estimates the materials and money needed to build a retaining wall. A retaining wall is a structure that holds back soil on a slope, so the ground on one side stays higher than the ground on the other side. The calculator takes the wall's height, width (length), and depth (thickness), works out its volume, and converts that volume into a number of bricks, stones, blocks, or timbers, along with a total material cost.

Retaining walls do two jobs. They stop soil from sliding or eroding, and they turn a sloped yard into flat, usable space. Material cost is usually 40 to 60 percent of the total project cost. Labor, drainage, permits, and site preparation make up the rest.

How to calculate retaining wall cost

The calculator works through three steps.

Step 1: Find the wall volume

$Volume (ft^3) = Height (ft) \times Width (ft) \times Depth (ft)$

Height is how tall the wall stands. Width is how long it runs. Depth is how thick it is, front to back.

Step 2: Find the number of units

$Units = \dfrac{Volume (ft^3)}{Volume\ per\ unit (ft^3)}$

Each material comes in a standard unit size. The calculator divides the wall's total volume by the volume of one unit, then rounds up, because a partial brick or block still means buying a whole one.

Step 3: Find the total cost

$Total\ Cost = Units \times Cost\ per\ Unit$

Material sizes used in the calculator

The volume of a single unit depends on its real-world dimensions, including the mortar joint between units where one applies.

The brick figure comes from a standard modular brick, 4 by 2⅔ by 8 inches including its mortar joint (Brick Industry Association, Technical Note 10). The concrete figure comes from a standard concrete masonry unit (CMU) block, 8 by 8 by 16 inches including mortar (ASTM C90 / National Concrete Masonry Association). Stone has no fixed industry size, so the calculator uses an average landscape stone volume as a working assumption. Cost ranges vary by region and supplier.

Example calculation

Take a wall 4 feet high, 10 feet long, and 1 foot thick, built from brick at $2.50 per brick.

1. Volume: 4 × 10 × 1 = 40 ft³
2. Units: 40 ÷ 0.0494 = 809.7, rounded up to 810 bricks
3. Cost: 810 × $2.50 = **$2,025**

The same 40 ft³ wall built from concrete block instead: 40 ÷ 0.5926 = 67.5, rounded up to 68 blocks. At $8.00 per block, that is$544.

Choosing a material

Brick gives a traditional look and suits small DIY walls, but it is usually limited to about 4 feet without engineering, and it needs mortar and masonry skill.

Stone is durable and blends into a landscape, but it is heavy, often costly, and irregular pieces make building slower.

Concrete block is strong, can reach greater heights, and needs little upkeep, though plain block can look plain and poured concrete needs forms and equipment.

Wood is the cheapest to buy and easiest to cut, but pressure-treated timber walls typically last only 7 to 15 years and need regular checks for rot and insect damage.

What the estimate leaves out

The calculator covers material cost only. A real project also needs:

• 5–10% extra material for cuts, waste, and breakage
• Mortar or adhesive, where the material requires it
• Drainage gravel, perforated pipe, and filter fabric behind the wall
• Labor, if the wall is not self-built
• Permits and engineering plans for taller walls

Frequently asked questions

How accurate is the retaining wall cost calculator?

It gives a reliable estimate of material quantity and material cost for the dimensions and material entered. Actual project cost depends on local prices, waste, and extras such as drainage or reinforcement, which the calculator does not include. Adding 10–15% on top of the calculated material cost is a reasonable safety margin.

What height of retaining wall needs a permit?

Rules differ by city and county, but many places require a permit, and sometimes an engineer's plan, once a wall passes 4 feet in height, measured from the bottom of the footing to the top of the wall. Some areas set a lower limit near property lines or in earthquake zones. Check with the local building department before starting.

How deep should a retaining wall foundation be?

A common rule of thumb is a foundation depth of at least one-eighth of the wall's height, with a minimum of 6 inches. A 4-foot wall would need at least a 6-inch deep foundation. In places with freezing winters, the foundation should sit below the frost line so frost heave does not push the wall out of place.

Which retaining wall material lasts the longest?

Well-built concrete and stone walls commonly last 50 to 100 years with little upkeep. Brick walls typically last 20 to 30 years. Wood walls have the shortest life, usually 7 to 15 years, depending on the wood and the local climate.

Do retaining walls need drainage?

Almost always, yes. Water that builds up behind a wall pushes on it and can cause it to fail. Standard drainage includes gravel backfill, a perforated pipe at the base, weep holes, and filter fabric to keep soil out of the drainage layer. The calculator does not price drainage materials, so budget for them separately.

How much material does a 4-foot by 20-foot wall need?

For a wall 4 feet high, 20 feet long, and 1 foot thick, the volume is 80 ft³. At typical cost-per-unit assumptions:

These figures cover materials only, not labor, drainage, or permits.

References

1. Brick Industry Association. Technical Note 10: Standard Modular Brick Sizes.
2. ASTM International. ASTM C90: Standard Specification for Loadbearing Concrete Masonry Units.
3. National Concrete Masonry Association. Design Manual for Segmental Retaining Walls (3rd ed.).
4. Das, B. M. (2018). Principles of Geotechnical Engineering (9th ed.). Cengage Learning.