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Retaining wall block calculator

Enter the wall and your block size from the label. Defaults are a common small wall block.

Enter your numbers to see the result.

A block wall is rows of blocks plus the parts you never see: a buried course, a compacted gravel pad and a column of drainage stone behind it.

How it works

  • Courses: (exposed height + buried depth) / block height, rounded up. The first course is buried 6 in or 10% of the wall height, whichever is more.
  • Blocks per course: wall length / block face length, rounded up. Add a few percent for cuts.
  • Leveling pad: a trench 12 in wider than the block and 6 in deep, filled with compacted 3/4 in minus base.
  • Drainage stone: 3/4 in clean, angular stone 12 in deep behind the blocks, the full height of the wall.

Before you build

  • Walls over about 4 ft, or walls holding up a driveway, slope or building, usually need an engineer and a permit. Check with your town.
  • Call 811 before digging.
  • Follow the block maker's guide: setback, adhesive for caps and geogrid rules differ by system.

Sources

Sources last checked 1 November 2026.

Frequently asked questions

How many retaining wall blocks do I need?

Divide the wall length by the block face length for blocks per course, then multiply by the number of courses, including the buried one.

How deep should the base be for a retaining wall?

At least 6 in of compacted 3/4 in minus gravel, per Belgard, with the first course buried 6 in or more.