Retaining Wall Block Calculator
Find blocks and courses for a retaining wall.
Default 12 in
Default 8 in
Default 5%
Results update as you type.
How it works
Building a segmental retaining wall requires knowing how many blocks to buy, and this calculator estimates the count and the number of courses from your wall dimensions. You enter the wall length and finished height, optionally set the block size and a waste allowance, and it returns the total blocks and how many rows, or courses, tall the wall will be. It works by figuring how many blocks fit in one course along the length, how many courses are needed to reach the height, and multiplying, then adding waste for cuts and breakage. Retaining wall blocks come in many sizes; the common default here is a 12-inch-long, 8-inch-high unit, but you should enter your actual block dimensions. Remember that a proper retaining wall includes a buried base course for stability, typically one full course below grade, so add height accordingly, plus cap blocks for the top and gravel backfill and drainage behind the wall. For walls taller than three or four feet, or those holding back significant loads, consult an engineer and local codes, since these often require special design, reinforcement, or permits. Use this estimate to order blocks for garden terraces, raised beds, and landscape walls. Enter your wall length and height to compute the blocks and courses.
Blocks = blocks per course × courses × (1 + waste)
The calculator divides the wall length by the block length to get blocks per course, and the wall height by the block height to get the number of courses, rounding each up. Multiplying the two and adding a waste allowance gives the total blocks. It counts the visible wall face; buried base courses and caps are handled separately.
Source:Masonry estimation
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter wall length and wall height.
- 2
Adjust the options
Adjust block length (in), block height (in) and waste allowance if they apply — sensible defaults are already set.
- 3
Read your result
Blocks needed updates instantly as you type — no button to press.
Frequently asked questions
How many blocks do I need for a retaining wall?
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, multiply the two, and add a waste allowance. The calculator does this from your dimensions and returns the total block count along with how many courses tall the wall will be.
Should I include a buried base course?
Yes. A stable retaining wall sets its first course below grade, typically buried about one-tenth of the wall height or at least one full course deep. When entering the wall height, include this buried portion so your block count covers the base course, which anchors the wall and resists sliding and frost heave.
What else do I need besides blocks?
Beyond the blocks, a retaining wall needs a compacted gravel base, gravel backfill behind the wall for drainage, a perforated drain pipe for taller walls, landscape fabric, and cap blocks with adhesive for the top course. Reinforced walls also use geogrid. Plan and order these materials separately once you know your block count.
How tall can I build without an engineer?
Many jurisdictions allow do-it-yourself segmental retaining walls up to about three to four feet before requiring engineered design and a permit. Taller walls, or walls supporting driveways, slopes, or structures, carry large loads and need professional design and reinforcement. Always check your local building code before starting, as limits and requirements vary.
Do I need cap blocks?
Cap blocks finish the top of the wall, giving it a clean edge and protecting the cores below from water. They are usually glued down with masonry adhesive. This calculator counts the main wall blocks; add a row of caps equal to the blocks per course, adjusted if the caps are a different length than the wall blocks.