Retaining Wall Calculator

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in
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Construction

Estimate number of retaining wall blocks and cap blocks needed.

Formula

Blocks = courses × blocks per course; courses = wall height / block height
  • Standard Allan Block (AB): 12 in long × 6 in high = 1.5 blocks/sq ft face area.
  • Add 5% for cuts and waste.
  • Walls over 4 ft typically require engineering review and geogrid reinforcement.

20 ft long, 3 ft high, 6×18 in blocks

Inputs
  • Wall Length: 20 ft
  • Wall Height: 3 ft
  • Block Height: 6 in
  • Block Length: 18 in
  • Setback per Course (%): 1 %

Courses: 6. Blocks/course: 14. Total: 84 × 1.05 = 89 blocks. 14 cap blocks.

Frequently asked questions

Do I need a permit for a retaining wall?
Most jurisdictions require a permit for walls over 4 ft from bottom of footing to top. Walls retaining surcharge loads (driveways, structures) may need one at lower heights.