Retaining Wall Block Calculator
A segmental retaining wall is a grid of blocks: rows called courses stacked to the wall height, each course holding a number of blocks across the wall length. Divide the wall length by the block length for blocks per course, divide the wall height by the block height for the number of courses, then multiply. Add a waste percentage for cuts and breakage. This calculator does that arithmetic from your measurements and block size, giving a block order you can take to the yard.
Retaining wall block formula
Blocks per course = ceil((wall length * 12) / block length inches)
Courses = ceil((wall height * 12) / block height inches)
Base blocks = blocks per course * courses
Total blocks = ceil(base blocks * (1 + waste / 100))
Wall length and height in feet are converted to inches to match the block dimensions. Blocks per course and courses are each rounded up because partial blocks and partial rows still require whole units. Waste is added as a percentage and the final order is rounded up.
Retaining wall notes
- Courses are the stacked horizontal rows; blocks per course span the wall length.
- Common segmental block faces are about 12 inches long and 4 to 8 inches high.
- A 5 to 10 percent waste allowance covers cuts at ends and corners plus breakage.
- Guidance often buries the base course about one tenth of wall height for stability.
- Cap blocks, base gravel, and drainage backfill are separate items not counted here.
Retaining wall blocks: frequently asked questions
How many blocks do I need for a retaining wall?
Divide the wall length by the block length to get blocks per course, and divide the wall height by the block height to get the number of courses. Multiply the two and round up. For a 30 foot long, 3 foot high wall using blocks 12 inches long by 6 inches high, that is 30 blocks per course times 6 courses, or 180 blocks before waste.
How do I count the number of courses?
Courses are the horizontal rows stacked to reach the wall height. Divide the finished wall height by the height of one block and round up, since a partial course still needs a full row. Most segmental retaining wall blocks are 4 to 8 inches tall, so a 3 foot wall is roughly 5 to 9 courses.
Should I add a waste allowance?
Yes. Cuts at corners and ends, breakage, and color blending mean you should buy a few percent extra. A common allowance is 5 to 10 percent. Enter your waste percentage and the calculator adds it to the base block count, rounding the final order up to whole blocks.
Does this include the buried base course?
The course count is based on the finished exposed wall height you enter. Engineering guidance often calls for burying the bottom course about one tenth of the wall height for stability. If you want to include the buried course, add that depth to the wall height before entering it so the course count covers it.
What about cap blocks and base gravel?
Cap blocks that finish the top and the compacted gravel leveling base are separate items not counted here. This calculator counts the wall body blocks only. Order caps to match your wall length divided by the cap length, and calculate base gravel separately by trench volume.
Official sources
- U.S. Federal Highway Administration: Mechanically stabilized earth wall guidance.
- U.S. National Institute of Standards and Technology: Unit conversion (foot, inch).
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.