Retaining Wall Block Calculator
Blocks, caps, courses and gravel for a segmental retaining wall from your block size, buried course, waste allowance, base depth and drainage width.
Courses (with the overshoot when the height does not divide), blocks per course, block and cap counts with waste, base and drainage gravel volumes — counts only, engineering left to you.
Example: A 30 ft wall 3 ft high with a 4 in buried course in 12 × 4 × 8 in blocks: 10 courses of 30 = 300 blocks, 315 with 5 % waste, 32 caps, 0.93 yd³ of base gravel and 3.33 yd³ behind the wall.
Courses, blocks, gravel —
counts only.
How courses and blocks are counted, what the gravel figures cover, and what the page deliberately leaves to you.
Counting
Courses = ⌈(exposed height + buried depth) ÷ block height⌉ — rounded up, with a note when the result stands proud of your target. Blocks per course = ⌈length ÷ block length⌉; cut blocks count whole. Blocks = courses × per course × (1 + waste). Caps = ⌈length ÷ cap length⌉ × (1 + waste). Block sizes come from the product because they differ between systems.
Gravel
Base gravel = length × (block depth + extra each side) × base depth; drainage gravel = length × zone width × exposed height. Both are volumes in yd³ or m³ before compaction; the Aggregate Tonnage utility turns them into tonnes.
Not decided here
Whether the wall needs a setback, geogrid, a drain pipe, engineering or a permit depends on its height, the soil and the retained load and on local rules. The page counts materials for the wall you describe; it does not say whether that wall is adequate. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Counting arithmetic: courses and blocks per course rounded up, gravel as length × width × depth (no design values; block sizes from the product)
Last reviewed 20 September 2026. How results are checked: How we verify.