Retaining Wall Calculator
Free retaining wall calculator. Enter wall length and height to get the number of wall blocks, cap blocks, base gravel, drainage gravel and drain pipe.
- Wall blocks
- 221
- incl. 5% extra
- Courses
- 7
- incl. 1 buried
- Cap blocks
- 42
- 12 in caps
- Block cost
- $1,799
Base and drainage
| Wall face | 120 sq ft |
| Blocks per course | 30 |
| Leveling base gravel24 in wide × 6 in deep trench | 2.1 t |
| Drainage gravel12 in zone behind the wall | 7.3 t |
| Perforated drain pipe4 in, at the base behind the wall | 40 ft |
Price
$1,799
Blocks and caps only, before gravel, pipe and delivery
Default prices are typical U.S. retail figures, reviewed November 2026. Enter your supplier's prices for an exact total.
Segmental retaining wall blocks are stacked in courses, with the first course buried below grade, and finished with cap blocks. How many you need depends on the wall length, the height and the face size of the block you choose.
Enter the wall length and height and pick a block size. The calculator counts courses, wall blocks and caps, and works out the gravel for the leveling base and the drainage zone behind the wall, plus the length of drain pipe.
How to use the retaining wall calculator
- Measure the wall length along the ground in feet.
- Decide the height above ground, then add one buried course.
- Divide the height in inches by the block height to get the number of courses.
- Divide the length in inches by the block width to get blocks per course.
- Multiply courses by blocks per course and add 5% for cuts and breakage.
Courses = height (in) ÷ block height + 1 buried. Blocks = courses × (length (in) ÷ block width) × 1.05. Caps = length (ft) × 1.05 for 12 in caps.
Blocks needed by wall size
Standard 16 × 6 in face blocks, one buried course, 5% extra.
| Wall | Wall blocks | Caps (12 in) |
|---|---|---|
| 20 ft long × 2 ft high | 79 | 21 |
| 20 ft long × 3 ft high | 111 | 21 |
| 40 ft long × 3 ft high | 221 | 42 |
| 40 ft long × 4 ft high | 284 | 42 |
| 60 ft long × 3 ft high | 331 | 63 |
Tips before you buy
- Set the first course on 6 inches of compacted gravel in a trench, and make it perfectly level; every course above follows it.
- Backfill the 12 inches behind the wall with clean drainage stone, not soil, and run a perforated pipe at the base.
- Most block makers limit unreinforced walls to about 3 to 4 feet; taller walls need geogrid and often an engineer.
- Call 811 before you dig.
Frequently asked questions
How many blocks do I need for a retaining wall?
Divide the wall face area by the face area of one block, then add a buried course and 5% extra. A 40 foot wall 3 feet high in 16 × 6 inch blocks needs about 221 blocks and 42 caps.
How much gravel do I need behind a retaining wall?
Plan on a 12 inch wide zone of drainage stone the full height of the wall. For a 40 foot wall 3 feet high that is about 5 cubic yards, or roughly 7 tons, plus about 2 tons for the leveling base.
How deep should the first row of a retaining wall be buried?
Bury about one inch for every 8 inches of wall height, with a minimum of one full course (about 6 inches) for most blocks.
How tall can a retaining wall be without reinforcement?
Most segmental block walls can go about 3 to 4 feet high without geogrid, depending on the block and the soil. Check the manufacturer's limits and your local code.