Retaining Wall Calculator
Enter the wall length, height, and block size to get wall blocks, cap blocks, courses, and gravel base.
Wall & block
Walls over ~3–4 ft usually need engineering, geogrid, and a permit.
You'll need
Courses (rows)0
Blocks per row0
Wall blocks
0
+5% waste
Cap blocks (top row)0
Gravel base (approx)0 yd³
Add drainage gravel and pipe behind the wall and a compacted leveling base below the first course.
How to estimate a retaining wall
Blocks per row = wall length ÷ block width; courses = wall height ÷ block height. Multiply for the block count, add ~5% waste, and add cap blocks for the top course plus a compacted gravel base and drainage stone behind the wall.
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Retaining wall FAQ
- How many blocks do I need for a retaining wall?
- Find blocks per row by dividing the wall length in inches by the block width, and the number of courses by dividing the wall height by the block height. Multiply the two and add ~5% for waste and cuts.
- How deep should the base of a retaining wall be?
- Bury the first course about 10% of the wall height (at least one full block or ~6 inches) and set it on 4 to 6 inches of compacted gravel base in a level trench.
- When does a retaining wall need engineering?
- Walls taller than about 3 to 4 feet, or any wall holding back a slope or surcharge, typically require an engineered design, geogrid reinforcement, and a permit. Check local code before building.
- What goes behind a retaining wall?
- Drainage gravel and a perforated drain pipe behind the blocks let water escape so hydrostatic pressure doesn't push the wall over. This drainage stone is separate from the leveling base.