Retaining wall block calculator
How many retaining wall blocks you need for a garden or landscape wall, course by course.
Blocks needed
- Wall area
- Per sq ft
How to use it
Enter the wall's length and its total height in feet, including the part buried below ground. Then enter your block's face size, the part you see from the front: the defaults are for a common 12 × 4 in landscape block. Retaining wall blocks usually stack dry, so the joint is 0.
How it's calculated
- Courses = wall height in inches ÷ block height, rounded up.
- Blocks per course = wall length in inches ÷ block face length, rounded up.
- Blocks = courses × blocks per course, plus the breakage allowance.
| Block face | Blocks per sq ft of wall face |
|---|---|
| 12 × 4 in | 3 |
| 16 × 6 in | 1.5 |
| 18 × 6 in | about 1.33 |
Building it to last
- Bury the first course. Most block makers call for the bottom course to sit below ground, often about an inch for every 8 inches of wall height, with a minimum of a few inches. Include it in the height you enter.
- Base: set the first course on a compacted gravel base, typically about 6 inches deep, so the wall stays level. The gravel calculator can size it.
- Drainage: backfill behind the wall with gravel and add a drain pipe for taller walls. Water pressure is the most common reason retaining walls fail.
- Height limits: many block systems and local codes limit unreinforced walls to about 3 to 4 feet. Taller walls usually need geogrid reinforcement, an engineer, or a permit.
- Caps: cap blocks for the top row are often sold separately. Count wall length in inches ÷ cap length.
Follow your block maker's installation guide: setback, base depth and maximum height differ between products.