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Retaining Wall Calculator
Find how many blocks a retaining wall needs.
Blocks needed
—
For the wall face.
| Courses (rows) | — |
|---|---|
| Blocks per row | — |
| Wall area | — |
| — |
Show our math
Enter your figures above to see the step-by-step working.
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How the Retaining Wall Calculator Works
Count the wall in courses (horizontal rows) and blocks per row. The number of courses is the wall height divided by the block height; blocks per row is the wall length divided by the block length — both rounded up, and both converted from feet to inches first. Multiply the two for the total. A 20-foot-long, 3-foot-high wall built from 18-by-6-inch blocks needs 6 courses of 14 blocks — 84 blocks.
This counts the visible wall face. Add blocks for a buried base course (recommended for stability), and plan on gravel backfill and a drainage pipe behind the wall. Cap blocks for the top row are counted separately.
blocks = ⌈height ÷ block height⌉ × ⌈length ÷ block length⌉
Frequently Asked Questions
How many blocks for a retaining wall?
Round up the height divided by block height for the number of courses, and the length divided by block length for blocks per row, then multiply. This calculator does it from your measurements.
Should I bury the first course?
Yes — burying the base course about one-tenth of the wall height (at least one course) anchors the wall. Add those blocks to the total.
Do I need drainage behind the wall?
Almost always. Gravel backfill and a perforated drain pipe relieve water pressure, which is the main cause of retaining-wall failure.