About this tool
The Retaining Wall Block Calculator estimates the materials for a segmental block retaining wall: the wall blocks, cap blocks, base leveling gravel and drainage backfill stone. Enter the wall length in feet, the exposed wall height in inches, your block dimensions (length × height × depth) or pick a preset, the cap block length, base gravel depth, drainage-zone width and a waste percentage. Everything is calculated in your browser.
The number of courses (rows) is the wall height divided by the block height, rounded up. Blocks per course is the wall length in inches divided by the block length, rounded up. Total wall blocks is courses × blocks-per-course with your waste allowance added, and cap blocks cover the top course at wall-length ÷ cap-length. Base gravel volume is wall length × trench width × base depth, where the trench is about twice the block depth; drainage backfill volume behind the wall is wall length × drainage-zone width × wall height. Both volumes are converted from cubic feet to cubic yards by dividing by 27.
Presets cover a common 12×8×12" unit and a larger 18×6×12" unit, or you can enter custom dimensions. As a rule, bury about one course (roughly 1" for every 8" of exposed height) so the wall resists frost heave and soil pressure — include that buried course in the height you enter. Walls over 4 feet tall generally require geogrid reinforcement and an engineer's review, so treat this as a material estimate rather than a structural design.