Retaining Wall Calculator

One of the most common questions during landscape construction is how many retaining wall blocks are required to complete a wall. The calculation involves finding the total surface area of the wall face and dividing it by the surface face area of a single block.

To determine this yourself, use the following formula:

Where Block Face Area is equal to (Block Length in inches × Block Height in inches) ÷ 144. Always add a waste factor of 5% to 10% to account for cut blocks, corners, and breakage during installation.

Landscape retaining walls are popular additions to yards for aesthetic and functional benefits. They stabilize steep slopes, prevent soil erosion, create tier-terraced flat lawns, and manage water runoff. Utilizing a block calculator guarantees you buy the correct quantity of materials in one trip, avoiding delays.

Whether you are building a small garden terrace using lightweight concrete stones or a massive structural wall, planning the base foundation depth, drainage backing, and geogrid layers ensures structural integrity and prevents tipping.

A retaining wall is only as strong as its foundation. Building directly on soil leads to settling, shifting, and wall collapse. Segmental retaining walls require a compacted leveling pad made of road base gravel (such as 3/4-inch crushed run or quarry process).

The base gravel pad must be a minimum of 6 inches thick and extend at least 6 inches wider than the block depth. Excavating the base trench, leveling the gravel pad, and thoroughly compacting it provides a solid lateral and vertical support structure.

Water is the number one cause of retaining wall failures. When rain and ground moisture collect behind a wall, it creates hydrostatic pressure. Without a path to escape, this pressure pushes against the back of the blocks, causing the wall to bow and eventually fail.

To prevent hydrostatic pressure, structural guidelines specify placing a 12-inch column of clean, crushed drainage gravel directly behind the blocks, along with a perforated drain pipe running at the bottom of the base. A drainage geotextile fabric wraps this stone column to prevent soil migration.

The zone directly behind the drainage aggregate is called the backfill zone. Backfilling with stable soil or extra gravel ensures load support. The backfill zone is excavated during site preparation, then replaced in 6-inch layers (lifts), compacting each lift thoroughly to minimize settling and lateral shifting.

For walls exceeding 3 to 4 feet in height, gravity alone is often insufficient to resist soil pressure. Structural engineers use geogrid sheets—a synthetic mesh material sandwiched between block courses that extends deep back into the backfill soil zone.

The geogrid physically anchors the retaining blocks back into the soil mass, turning the soil itself into a reinforced block structure. The length of the geogrid layers should extend back at least 70% of the wall's total height.

The total cost of your retaining wall depends on the blocks selected, base and drainage materials, geogrid sheets, flat mobilization rates, and labor. Using this cost estimator lets you simulate budgets based on linear footage pricing, block counts, and flat contractor fees.

When deciding on wall materials, consider block vs concrete. Segmental block systems are flexible, require no concrete footings, are DIY-friendly, and handle minor settlement. Poured concrete walls are rigid, extremely strong, and ideal for commercial heights, but require extensive steel rebar, footings, and specialized labor.

• Garden Retaining Wall: A decorative 20' × 3' border using standard 12" blocks to raise garden beds.
• Landscape Wall: A 40' × 4' tier wall utilizing geogrid layers and cap blocks to stabilize a backyard slope.
• Slope Stabilization Wall: A 50' × 6' heavy structural segmental block wall with a deep compacted base and gravel drainage backing.
• Commercial Retaining Wall: A 100' × 8' tall industrial wall requiring engineered segmental blocks and multiple geogrid layers.