Retaining Wall Block Calculator
Enter a wall's length and height and your block and cap sizes and get retaining wall blocks by whole courses and caps along the top, rounded up once, with the working shown for an example wall. It counts blocks and caps only.
Estimates for planning, not professional advice. Read the full notice.
Example: a garden wall
126 blocks
- Courses of block under the cap 6 courses
- Laid height of the blocks 3 ft
- Blocks if the cut pieces were all reused, exact 120 blocks
- Whole blocks per course times courses (the count the buy uses) 120 blocks
- Caps to buy 21 caps
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Your project
Enter a size to see your total.
Each product is rounded up once for the whole project, so the total can be less than the items bought alone added together. A line counted from a cut layout (sheets, boards or tiles laid out piece by piece) is counted for each item and added.
Shopping list
| Item | Size | Buy |
|---|---|---|
| Wall blocks | blocks | 126 |
| Caps | caps | 21 |
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Worked example: a garden wall
Show the working
- Height under the cap: wall height less the cap height 3 ft − 4 in = 2 ft 8 in
- Courses: that height divided by one block's height 2 ft 8 in ÷ 6 in = 5.33 courses
- A course is a whole row, so round up 5.33 courses = 6 courses
- Whole blocks in one course: wall length over one block's length, rounded up 20 ft ÷ 1 ft = 20 blocks
- Whole blocks: courses times blocks in one course 6 courses × 20 blocks = 120 blocks
- Add the waste allowance and round up once 120 blocks × 1.05 = 126 blocks
- Caps: whole caps along the wall, with waste, rounded up once 20 caps × 1.05 = 21 caps
Assumptions
The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.
| Assumption | Value | Details and changes |
|---|---|---|
| Wall block waste allowance | 5% | |
| Default Your own allowance. No source is cited for it here; check your block label or supplier. | ||
Feet and inches, like 12' 6"
Courses and laid height against the wall height
Whole courses, the laid height of the blocks and the blocks and caps for the example wall at several wall heights
| Wall height | Courses | Laid height of the blocks | Whole blocks per course | Blocks to buy | Caps to buy |
|---|---|---|---|---|---|
| 2 ft | 4 courses | 2 ft | 20 blocks | 84 blocks | 21 caps |
| 2 ft 6 in | 5 courses | 2 ft 6 in | 20 blocks | 105 blocks | 21 caps |
| 3 ft | 6 courses | 3 ft | 20 blocks | 126 blocks | 21 caps |
| 3 ft 6 in | 7 courses | 3 ft 6 in | 20 blocks | 147 blocks | 21 caps |
| 4 ft | 8 courses | 4 ft | 20 blocks | 168 blocks | 21 caps |
| 5 ft | 10 courses | 5 ft | 20 blocks | 210 blocks | 21 caps |
A course is a whole row, so the laid height can differ from the height typed. The courses always cover the height under the cap, so the laid height is never below it. Block and cap sizes and the waste allowance are the example's.
Questions
How many retaining wall blocks do I need?
Type the wall's length and height and the size of your block, and the calculator counts the courses under the cap, the blocks across the wall for those courses and the caps along the top, each rounded up once with your waste allowance.
Why do the courses round up?
A course is a whole row of blocks. When the height under the cap does not divide evenly by the block height, the last course still has to be laid, so the count goes up to the next whole course.
Are caps counted separately?
Yes. Type the cap's length and height and the blocks are counted up to the cap, with caps counted along the wall's length. Leave the cap fields blank for a wall with no cap.
Does it check that the wall is tall or strong enough?
No. It counts blocks and caps from the sizes you type. Walls taller than a local limit may need an engineer's design, so ask your building department.