Retaining wall calculator
PROBlocks, base gravel and cost for a segmental retaining wall.
Short answer: Rows = ⌈height ÷ block height⌉. Per row = ⌈length ÷ block length⌉. 20 ft × 24" high, 12×4" blocks = 6 rows × 20 = 120 blocks. Enter your measurements above and the retaining wall calculator returns the quantity, unit conversions and an estimated cost instantly, in imperial or metric — no sign-up needed.
What do you need to measure?
What is the answer?
Blocks
120
6 rows × 20
Base gravel
0.19 yd³
Est. cost (blocks)
$480
How does the retaining wall calculator work?
Rows = ⌈height ÷ block height⌉. Per row = ⌈length ÷ block length⌉.
What does a worked example look like?
20 ft × 24" high, 12×4" blocks = 6 rows × 20 = 120 blocks.
What do people ask most?
›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.
Which outdoor construction calculator should you use next?
Where can you learn more?
Read field notes on estimating and materials, or browse every calculator we make.