Enter wall length, height and your block’s face size to see how many retaining-wall blocks and cap blocks to buy — with the permit line flagged.
How wall blocks are counted
A segmental retaining wall is counted by face area: the wall’s length times height, divided by the face of one block. Enter your dimensions and the block’s face size from its product listing, and this calculator returns the block count, the cap blocks for the top course, and — because it matters more than the math — a flag when the height crosses into engineering territory.
How to use it
- Enter the wall length and height in feet.
- Enter the block’s face length and height in inches (12×4 is a common size).
- Add 5–10% for cuts and curves when ordering.
The formula
A worked example
A 20 ft wall at 3 ft high is 60 sq ft of face; with 12×4-inch blocks (a third of a square foot each) that is 180 blocks plus 20 caps. The count is the easy part — the wall’s longevity lives underground: a compacted gravel base course below grade, and gravel backfill with drainage behind, neither of which appears in the block math but both of which decide whether the wall stands in ten years.
An honest boundary
Walls above roughly 3–4 feet — lower in some jurisdictions, or any height holding a slope or surcharge — commonly require engineering and permits. Check local code before building tall; a failed retaining wall is a genuinely dangerous thing.