Block sizes are nominal and vary between brands, so enter the face length, height and depth from the spec sheet of the block you plan to buy.
How the retaining wall calculator works
RetainingWallCalc divides the wall length (in inches) by the block face length and rounds up to get the blocks per course. It divides the exposed height by the block height for the courses above ground, then adds enough buried courses to reach the bury depth: 1 inch per 8 inches of exposed height, at least 6 inches. Blocks = blocks per course × courses, plus your waste allowance. Caps = wall length ÷ cap length, plus the same allowance.
The base trench is the block depth plus the extra width you set (12 inches gives 6 inches in front and behind), at the base depth, plus a compaction allowance. Drainage stone fills a zone behind the blocks for their full height. Cubic yards are converted to tons with the density you enter.
Typical block sizes
| Block (face × height × depth) | Blocks per sq ft of face | Typical use |
|---|---|---|
| Small garden wall block 12 × 4 × 7 in | 3 | Garden edging, raised beds, walls to about 2 ft |
| Medium retaining block 16 × 6 × 10 in | 1.5 | Landscape walls to about 3 ft |
| Large retaining block 18 × 8 × 12 in | 1 | Retaining walls to about 4 ft without geogrid (check the maker) |
Bury depth by wall height
| Exposed height | Minimum buried block |
|---|---|
| 2 ft (24″) | 6″ |
| 3 ft (36″) | 6″ |
| 4 ft (48″) | 6″ |
| 5 ft (60″) | 7.5″ |
| 6 ft (72″) | 9″ |
Bury depth, 6-inch base and 12-inch drainage zone are common manufacturer guidance for segmental block walls; your block system's installation guide wins. Walls retaining more than 48 inches of soil need an engineered design under the IRC (R404.4), as do walls with slopes, driveways or buildings above them. Results are estimates: confirm quantities with your supplier and call 811 (US) before you dig.
Frequently asked questions
How many blocks do I need for a 30 ft wall 3 ft high?
With 16 × 6 inch blocks: 23 blocks per course × 7 courses (6 above ground and 1 buried) = 161 blocks, or 170 with 5% extra.
How do I calculate retaining wall blocks?
Blocks per course = wall length in inches ÷ block face length, rounded up. Courses = height in inches ÷ block height, rounded up, plus the buried courses. Multiply the two and add a few percent for cuts.
Do I count the buried course?
Yes. The first course sits below grade on the base, so it adds to the block count but not to the visible height.
Is RetainingWallCalc free?
Yes, with no sign-up or ads.
Are my measurements saved?
Yes, in this browser only.