Retaining wall calculator
PROBlocks, base gravel and cost for a segmental retaining wall.
Inputs
Result
Blocks
120
6 rows × 20
Base gravel
0.19 yd³
Est. cost (blocks)
$480
The formula
Rows = ⌈height ÷ block height⌉. Per row = ⌈length ÷ block length⌉.
Worked example
20 ft × 24" high, 12×4" blocks = 6 rows × 20 = 120 blocks.
Frequently asked
›Do I need drainage?
Yes — 4" perforated pipe + 12" of clean gravel behind walls over 2 ft.
›Max unreinforced height?
Most segmental block systems: 3–4 ft without geogrid.