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?
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.
What should you read before you order materials?
Field notes from real jobs that explain the numbers behind this calculator.