Retaining Wall Block Calculator
Enter the length and height of the wall and the face size of your block to see how many courses, blocks and cap blocks you need, plus the cubic yards of drainage gravel behind the wall.
How to use this retaining wall block calculator
- Enter the length of the wall and its visible height in feet.
- Enter the face length and face height of one block in inches.
- Enter how many courses will be buried below grade. Check the block maker for their rule.
- Enter the cap block length if you will use caps, and the depth of the drainage gravel behind the wall.
- Keep or change the waste allowance and press Calculate.
How to calculate retaining wall blocks
The calculator stacks courses up the height and lays blocks along the length.
- Visible courses = visible height (in) / block height, rounded up
- Total courses = visible courses + buried courses
- Blocks per course = wall length (in) / block length, rounded up
- Blocks = courses x blocks per course x (1 + waste % / 100), rounded up
- Caps = wall length (in) / cap length, rounded up
- Gravel = length x height x gravel depth (ft) / 27 cubic yards
Worked example
A wall is 30 ft long and 3 ft high. The blocks have a 12 inch by 4 inch face. The visible height is 36 inches, so there are 9 visible courses, and with 1 buried course the wall has 10 courses. Each course has 360 / 12 = 30 blocks, so the exact count is 300 blocks. With 5% waste you buy 315 blocks. The caps along the top are 30. The gravel behind the wall is 30 x 3 x 1 / 27 = 3.33 cubic yards.
Assumptions & limits
- The wall is straight and has the same height along its length. Curves, corners, steps and tapered walls need more blocks and cuts.
- The block face size is the real size you enter. The calculator does not look up product data.
- The gravel depth, buried courses and cap size are editable placeholders. They come from the block maker, plans or local rules.
- Geogrid, base gravel under the first course, drain pipe, fabric and adhesive are not counted.
- Taller walls and walls that hold back a slope or a load need engineering and often a permit. This calculator counts material only.
Frequently asked questions
How do I calculate how many retaining wall blocks I need?
Divide the wall height by the block height to get the courses, divide the wall length by the block length to get blocks per course, and multiply the two. Add waste.
Should I bury the first course?
Many block makers call for a buried base course. The calculator lets you enter how many courses are buried, so follow the maker instructions for your block.
How much gravel goes behind a retaining wall?
Use the depth in the block instructions or your plans. The calculator turns your depth, length and height into cubic yards.
How many cap blocks do I need?
Divide the wall length by the cap length and round up.
Do I need a permit for a retaining wall?
Many places require one above a certain height or near buildings or property lines. Check your local building department.
Does it work for curved walls?
Not exactly. A curve uses more blocks and more cuts. Add a larger waste percentage and ask the block maker.
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Last updated: November 2026