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Landscape Retaining Wall Calculator

Estimate retaining wall blocks, base gravel, and drainage for landscape walls. Enter wall length and height for block count and backfill materials.

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Inputs that matter
Wall Length, Wall Height, Block Length, Block Height
Output to expect
Retaining Wall Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Block Count

Wall face area = length × height. Divide by one block face area. Add 5% for cuts and caps.

Blocks = ceil(Wall Face Area ÷ Block Face Area × 1.05)

Gravel Base Trench

Buried course plus 6″ compacted gravel base in trench width of 24″ minimum.

Base (cu yd) = Length × Trench Width × Depth ÷ 27

Drainage Aggregate

Free-draining aggregate behind wall to daylight or drain pipe. Critical for hydrostatic pressure relief.

Drainage = Wall Height × Length × 12″ thick ÷ 27 cu yd

Updated: July 2026

Example Scenarios

120 sq ft face with 12×4×8″ blocks ≈ 540 blocks + cap units. No geogrid typically under 3 ft in stable soil.

4 ft height may need geogrid every 2 courses per manufacturer. Engineer required over 4 ft in many jurisdictions.

Curved wall uses more cut blocks — 10% waste. Compact base trench on undisturbed soil.

FAQ

Most segmental block manufacturers allow DIY to 3–4 ft with proper base and drainage. Over 4 ft typically requires engineered design and permits.

Yes for walls over 18″ — perforated pipe at base behind wall draining to daylight. Without drainage, hydrostatic pressure collapses walls.

Excavate to firm subgrade. 6″ compacted gravel base, level front-to-back and side-to-side. First course partially buried.

Manufacturer specs require geogrid reinforcement at height thresholds (often every 2 ft above 3 ft). Grid extends into retained soil 60–80% of wall height.

Cap blocks finish the top course and glue with concrete adhesive. Order caps = wall length ÷ cap length, rounded up.

About Landscape Retaining Wall Calculator

Plan segmental retaining wall materials before starting a garden or terrace project. Enter wall length, height, and block dimensions to get block count, gravel base, drainage aggregate, and geogrid layers for walls over 4 ft.