Retaining Wall Block Calculator
Enter wall length and height plus block dimensions to get block count, cap blocks, and gravel backfill volume.
Wall
Block Size
Materials Needed
How to estimate wall blocks
Block count = (wall length ÷ block length) × (wall height ÷ block height). This calculator adds a small waste factor for cuts at corners and ends. Cap blocks run one course on top: (wall length ÷ cap block length), typically the same length as the wall blocks. Gravel backfill fills the 6–12" space behind the wall for drainage — standard practice is 6" of ¾" clean crushed stone.
Height limits and engineering
Retaining walls above roughly 3–4 feet commonly require engineering and permits. The exact threshold varies by jurisdiction — some require permits above 30 inches, some above 4 feet, and slopes above the wall or surcharge loads (driveways, buildings near the top) trigger stricter requirements everywhere. Above threshold, walls typically need engineered geogrid reinforcement, deeper footings, and inspection. Check your local building department before starting.
The base is the wall
The single most important part of a retaining wall is the base — a level, well-compacted trench of ¾" crushed gravel, typically 6–8" deep, extending 6" wider than the wall on each side. Skipping this step or building on native soil is how walls lean, crack, and fail. This calculator estimates blocks and backfill but does not size the base or footing — use manufacturer install guides or a landscape engineer.