MEASURE. ESTIMATE. BUILD.
Count segmental retaining-wall blocks for your project.
Change any measurement to update your estimate.
Enter wall length, height, and your block size to get total blocks and the number of courses.
Segmental wall blocks stack in courses, so this view reports both the block count and the number of courses. Get the base course dead level — every course above inherits its errors, and walls over 3–4 feet usually need an engineer.
The base course is the whole wall — spend your time leveling the gravel pad, because every course above copies its errors. Bury the first course at least one block-height below grade so the wall can't kick out at the bottom. The calculator sizes a base one block wider than the wall and 6 inches deep for exactly this reason. Anything over 3–4 feet usually needs an engineer and a permit; check locally before you dig.
The math behind the tool:
blocks = (wall length ÷ block width) × (wall height ÷ block height)Sources: Concrete Masonry & Hardscapes Association (segmental retaining wall installation (formerly ICPI/NCMA)).
Divide the wall length by the block width and the wall height by the block height, then multiply the two. A 20 ft long, 3 ft high wall with 12×6 in blocks needs about 120 blocks.
Plan on a compacted gravel base about 6 inches deep and one block-width wider than the wall; the calculator returns this base volume in cubic yards.