Guide
How many retaining wall blocks do I need?
Courses for the height, blocks for the length, then what goes behind and under the wall.
The blocks
- Courses = wall height ÷ block height, rounded up.
- Blocks per course = wall length ÷ block length, rounded up, plus one to finish the course.
- Blocks = courses × blocks per course, plus 5 % for breakage and cuts.
Example
A wall 20 ft long and 2 ft high, with blocks 11¾ in long and 4 in high: 6 courses of 22 blocks, 132 blocks, 139 with 5 %. Caps of 12 in along the top: 23.
Behind and under the wall
- Drainage gravel behind it, 12 in wide over the full height: 40 cu ft, 1.48 cu yd, and 20 ft of drain pipe.
- Base: a trench of crushed stone 6 in deep, wider than the block on each side.
Taller walls need geogrid and often an engineer: follow the block maker's guide.
With Landscaping Calc
A wall zone counts the blocks, caps, drainage gravel, drain pipe and base from the length you measure or type. See Retaining wall calculator.
