Retaining wall calculator
Work out blocks per course, courses and total blocks for a retaining wall from wall dimensions and block size, including the buried base course.
Blocks needed
Enter your measurements and the result updates as you type.
Overview
A block retaining wall adds up in two directions: how many blocks span the wall length per course, and how many courses tall the wall stands. This calculator returns blocks per course, courses and the total block count from your wall dimensions and block size.
The first course is traditionally buried below grade, a full course taller than the finished height, and that extra course is built into the total so your order is really enough to build the wall.
Common mistakes
- Forgetting the buried base course, which means the delivered blocks fall one course short on day one.
- Dividing the wall length by the block length and rounding down, which leaves the last span short.
- Planning the block order without the drainage gravel behind the wall, which is where failure starts on a simple wall.
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In-depth guides
Frequently asked questions
How many blocks do I need for a 20 by 2 foot wall with 16-inch blocks?
Each course needs 15 blocks (240 inches divided by 16 inches), the wall stands 3 courses tall at 8-inch block heights, and with the buried base course that is 4 courses, so 60 blocks total.
What is the retaining wall block formula?
Blocks per course is the wall length (in inches) divided by the block length, rounded up. Courses is the wall height (in inches) divided by the block height, rounded up, plus one buried base course. Total is the product of the two.
Why is there an extra buried course?
The bottom course is set below grade so the wall does not work its way up and out as the soil behind it pushes forward. Standard practice for the block walls this calculator models is one full buried course under the finished height.
How much drainage gravel goes behind a wall?
A common spec is roughly a foot of clean drainage stone behind the block plus gravel-filled cores, the same crushed stone this site's gravel calculator measures. The block count here covers only the blocks; run the gravel calculator for the behind-wall tonnage.
How deep should a retaining wall footer be?
For small block walls, level compacted soil or a lightly dug trench is the usual base, with the buried course sitting on it. Taller engineered walls need real footings and engineer sign-off, so this calculator's models cap at the block-scale wall and defer to a professional above it.
Is there a height limit on retaining walls without a permit?
Many municipalities start requiring review around 4 feet of retained height, but the exact limit is local, so check with your building department rather than trusting a universal number.
How much does a retaining wall cost?
Block type and region swing the number widely, and drainage gravel and base are real line items. Run your block tally and the gravel volume, then apply your local block and gravel prices for a defensible total.
Do blocks at course ends need to be cut?
The formula rounds up so every course is whole blocks, which means a cut block at one end only when the span does not divide evenly. Keeping the wall length in whole block increments avoids those cuts entirely.