CALCULATION METHOD
How many retaining wall blocks do I need?
Divide wall length by block face length to find blocks per course. Divide exposed height by block face height and round up, then add buried courses. Multiply blocks per course by total courses and add the selected cutting allowance.
Blocks per course = wall length ÷ block face length, rounded up
Total courses = exposed height ÷ block height, rounded up + buried courses
Order blocks = blocks per course × total courses × (1 + waste)
Cap blocks = wall length ÷ cap coverage × (1 + cap waste)
20 × 3 ft retaining wall example
A 20 ft wall using 16 × 6 in block needs 15 blocks per course. A 3 ft exposed height is six courses; adding one buried course makes seven. That is 105 installed positions, or 111 blocks after a 5% allowance. Twelve-inch cap coverage requires 21 caps after 5% extra.
Retaining wall block calculator
Use the exact block’s face dimensions rather than nominal package names. Curves, corners, steps, grade changes, partial courses, columns, and pattern walls require additional units beyond a simple rectangular estimate.
Retaining wall gravel calculator
Base aggregate is calculated from trench length, width, and compacted depth, then multiplied by the loose aggregate factor. Drainage rock is estimated as a rectangular zone behind the exposed wall. Blocks with open cores can require additional aggregate not included here.
Backfill and drainage
The additional backfill field gives a simple rectangular planning volume beyond the drainage-rock zone. Real backfill follows the cut slope and engineered reinforcement zone, so approved plans take priority. Drainpipe, outlets, filter fabric, and water management are not quantified.
Retaining wall cost calculator
The material total includes blocks, caps, bulk base aggregate, bulk drainage rock, and optional backfill soil using the entered prices. It excludes labor, excavation, delivery, tax, adhesive, drainpipe, geotextile, geogrid, equipment, disposal, permits, and engineering.
Allan Block’s material estimation worksheet for blocks per course, courses, buried units, 5% extra, and aggregate planning; The Home Depot retaining wall guide for block-course estimating, embedment, drainage, and extra material; Belgard installation guidance for drainage aggregate and site-specific design. Accessed September 11, 2026.