Retaining wall block calculator
Segmental retaining wall blocks stack without mortar, each course set back slightly by a lip on the back of the block. The count is courses × blocks per course:
- Courses — exposed height ÷ block height, rounded up, plus one buried course below grade.
- Blocks per course — wall length ÷ block length, rounded up.
- Extra — 5% for broken blocks and the cuts at ends and curves.
| Wall | Small blocks (4 × 11.75 in) | Large blocks (8 × 18 in) | Caps |
|---|---|---|---|
| 10 ft × 1 ft high | 47 | 23 | 11 |
| 20 ft × 1.5 ft | 133 | 59 | 21 |
| 30 ft × 2 ft | 228 | 84 | 32 |
| 40 ft × 2 ft | 302 | 114 | 42 |
| 30 ft × 3 ft | — (too tall) | 126 | 32 |
Caps are about one per foot of wall. Small garden blocks like Pavestone's RockWall cover about 0.32 sq ft of face each and are rated for low walls only; large blocks like Allan Block's 8 × 18 in units cover about 1 sq ft each.
Retaining wall calculator cost: what to price
The blocks are the biggest line, but not the only one. For an accurate cost estimate, price each of these:
- Blocks and caps — enter your store's price per block and per cap under Prices for a cost estimate.
- Base gravel — about 6 in of compacted crusher run in a trench roughly 24 in wide; for the 30 ft wall above, about 2 tons.
- Drain rock — 12 in of clean #57 stone behind the blocks, full height; about 3.5 tons for the same wall. This is what keeps water from building up pressure behind the wall.
- Landscape fabric between the drain rock and the soil, and drain pipe for taller walls or clay soil.
- Delivery — a pallet of small blocks weighs well over a ton.
The gravel calculator prices the stone by the ton with delivery, and the shopping list here carries every item into a project list.
How tall can you build it yourself?
Our firm line: build gravity walls you can step over. Small blocks are rated for about 2 ft; heavier 8 × 18 in blocks go higher as gravity walls, but past about 3 ft most systems need geogrid layers tied back into the soil, and Allan Block calls for a perforated drain pipe at the base of walls over 4 ft or in clay. Many towns require a permit or an engineer's stamp above 4 ft, and so does common sense: a failed wall moves a lot of soil.
For a big grade change, two shorter walls with a planted terrace between them are often cheaper and safer than one tall wall. Leveling the area above the wall? The topsoil calculator handles the fill, and the paver calculator sizes a patio on top.
