How it works
Enter the wall length and exposed height and the face size of your block. The calculator counts courses (adding one buried course below grade), blocks per course, cap blocks, and the gravel needed for the base and drainage zone.
Manufacturers recommend burying the first course, or about one-eighth of the wall height, so the wall cannot kick out at the bottom. The leveling pad is typically a trench 24 inches wide and 6 inches deep filled with compacted crushed stone.
Fill at least 12 inches behind the wall with clean drainage stone and run a perforated drain pipe at the base so water pressure does not build up. Most block makers limit unreinforced walls to 3 to 4 feet; taller walls need geogrid and often a permit.
Formula
Courses = ⌈height × 12 ÷ block height⌉ + 1 buried. Blocks = courses × ⌈length × 12 ÷ block length⌉ × (1 + waste).
Questions people ask
How many retaining wall blocks do I need per square foot?
For a 12 × 4 in face, three blocks per square foot of wall face. A 16 × 6 in block works out to 1.5 per square foot.
How deep should the first course be buried?
At least one full course, or about 1 inch for every 8 inches of wall height, whichever is more.
Do I need gravel behind a retaining wall?
Yes. A 12 inch zone of clean, angular drainage stone behind the blocks, with a perforated pipe at the base, keeps water from building pressure and pushing the wall over.
How tall can a block retaining wall be without reinforcement?
Typically 3 to 4 feet for most small segmental blocks, less if there is a slope or driveway above. Many towns require a permit and engineering above 4 ft.