How to use the retaining wall block calculator calculator
- 1
Measure the wall length
Measure along the face of the wall. For a wall that turns a corner, measure each straight run separately, since corners often need their own blocks.
- 2
Decide the height you are entering
Enter the height of wall face you are building. If your plan includes buried courses below grade, include them here, because they use blocks too.
- 3
Enter the block face size
Use the face length and height of the block you are buying. Many wall blocks taper toward the back, so use the face dimensions, which are what shows and what sets the layout.
- 4
Add caps if the wall has them
Tick the cap option to add one course of cap blocks across the wall length. Caps are a different product and are counted separately from the wall blocks.
- 5
Add an allowance and price it
Add a percentage for cuts at ends and corners and for breakage, then enter your price per block for an estimated total.
Formula
Blocks = floor(wall height(in) / block height(in)) x (wall length(in) / block length(in))
Courses round down because a partial course is not built. Blocks per course stay exact so the total rounds up once at the end.
Worked example
A wall 40 feet long and 3 feet high, using blocks with a 12 inch face length and an 8 inch height
- 1Wall height in inches: 3 x 12 = 36 in.
- 2Courses: floor(36 / 8) = 4 courses, reaching 32 inches of the 36.
- 3Wall length in inches: 40 x 12 = 480 in.
- 4Blocks per course: 480 / 12 = 40.
- 5Total: 4 x 40 = 160 blocks.
The wall takes 160 blocks over four courses. The four courses reach 32 inches, so the last four inches of the entered height are not covered by a whole course.
Worked examples
Adding a cap course
The same 40 foot wall with a course of caps on top
- 1Blocks per course: 40.
- 2Cap blocks: one course across the wall length, so 40 caps.
- 3Wall blocks stay at 160.
- 4Total units to order: 160 wall blocks plus 40 caps.
Caps are counted separately because they are a different product with a different price. The calculator lists them on their own line.
When the height does not divide evenly
A 3 foot 4 inch wall with the same 8 inch block
- 1Wall height in inches: 40 in.
- 2Courses: floor(40 / 8) = 5 courses exactly, reaching 40 inches.
- 3Compare with the 36 inch wall: floor(36 / 8) = 4 courses reaching 32 inches.
- 4The extra 4 inches of height buys a whole additional course.
Wall heights that land on a course boundary use blocks efficiently. Heights that fall just short of one waste the remainder, which is worth knowing before the height is fixed.
Why courses round down
A wall is built in whole courses. You cannot lay four and a half courses of block, so the course count is the wall height divided by the block height with the remainder discarded.
The calculator shows both the course count and the height those courses actually reach, because the gap between them is useful information. A 36 inch wall built from 8 inch blocks reaches 32 inches in four courses. Whether that is fine, or whether the height should change to suit the block, is a decision for you rather than the arithmetic.
Blocks across a course are handled differently. Those stay exact through the calculation and only round up at the very end, so a wall needing 40.3 blocks per course over four courses rounds once at 162 rather than four times at 164.
Buried courses and exposed height
Most retaining wall designs bury the first course, or more than one, below finished grade. Those buried blocks are real blocks that have to be bought, but they do not show in the exposed height you measure above ground.
That creates an easy undercount. If your plan calls for one buried course and you enter only the exposed height, the block count comes up one course short across the whole wall length, which on a long wall is a substantial number.
Enter the full height of wall face being built, buried courses included, and note what that figure represents. How many courses should be buried is a design decision from your plan, not something this page determines.
What else a wall needs
The block count is one line of a retaining wall order. A wall also needs a compacted base beneath the first course, drainage aggregate behind the face, and often a drain pipe at the bottom, all of which are volume estimates rather than counts.
Corners, ends, and any curve in the wall usually need cut or specially shaped blocks. Curved walls in particular consume more blocks per foot on the outside of the curve than a straight run does.
Estimate the base and drainage stone with the gravel calculator, and take the quantities and depths from your wall design rather than from a general rule.
Common mistakes
Where retaining wall counts go wrong:
- Entering only the exposed height when the design also has buried courses.
- Using the back dimension of a tapered block instead of the face.
- Forgetting cap blocks, or counting them as ordinary wall blocks.
- Treating a wall that turns a corner as one straight run.
- Assuming a curved wall uses the same blocks per foot as a straight one.
- Ordering the exact count with no allowance for cuts at ends and breakage.
- Treating a block count as confirmation that the wall design is sound.
Sources and methodology
Every figure on this page comes from geometry rather than from a product database. Areas use the standard area formulas, counts divide an area by the size of one unit, and unit conversions use exact factors: 12 inches to a foot, 9 square feet to a square yard, and 100 square feet to a roofing square.
YardCalc publishes no product dimensions, coverage rates, or prices. Unit sizes differ between manufacturers and regions, and a figure that is right for one product is wrong for another, so the calculator asks you for the size of the product you are actually buying. Prices are yours alone.
Results are planning estimates, not order quantities. Read how every value on the site is derived and checked in the YardCalc calculation methodology.
Frequently asked questions
- How many blocks do I need for a retaining wall?
- Divide the wall height by the block height for courses, rounding down, then divide the wall length by the block length for blocks per course, and multiply. A 40 foot wall 3 feet high using a 12 by 8 inch block face takes 160 blocks over four courses.
- How high can I build a retaining wall?
- This calculator does not answer that. Maximum height depends on the soil, the slope above and below, the drainage, the block system, and local code, and many jurisdictions require an engineer or a permit above a certain height. Ask a qualified designer or your building department.
- Should I include buried courses?
- Yes, if your design has them. Buried blocks still have to be bought. Enter the full height of wall face being built rather than just the part that shows above grade.
- Why do courses round down but blocks per course do not?
- Because a partial course is never built, while a partial block across a course is simply a cut block. Keeping the per-course figure exact means the total rounds up once at the end instead of accumulating rounding on every course.
- Does this include base material and drainage stone?
- No. Those are volume estimates. Use the gravel calculator for the compacted base and the drainage aggregate, taking the depths and quantities from your wall design.
- How do I handle a curved wall?
- Measure along the face of the curve rather than across the chord, and expect to use more blocks per foot than a straight run because of the cuts a curve requires. Add an allowance that reflects how tight the curve is.
Course counts are the wall height divided by the block height you enter, rounded down; blocks per course are the wall length divided by the block length you enter. No block size, wall height limit, base depth, drainage detail, or price is assumed, and nothing here constitutes wall design. Counts come from exact geometry using the product dimensions you enter. Confirm the product size, the layout, cutting and breakage, and the final order quantity with your supplier before purchasing.
Results are planning estimates. Last reviewed 2026-08-30.