Retaining Wall Calculator
Estimate blocks, caps, base gravel and drainage gravel for a segmental retaining wall.
About the Retaining Wall Calculator
Segmental block walls sit on a compacted gravel base, usually with the first course buried for stability, and need free-draining gravel behind the blocks so water pressure doesn't push the wall over. Typical guidance from block manufacturers: a base 6 in (150 mm) deep and about 12 in wider than the block, one buried course per 8 in of exposed height, and 12 in of drainage gravel behind the wall with a perforated pipe at the base.
The formula
Blocks = ⌈wall length ÷ block length⌉ × (⌈height ÷ block height⌉ + buried rows)
Worked example
Example: Wall blocks = 154 + 5–10% spare
- Inputs: Units: Feet / inches; Wall length: 33; Wall height: 3; Block face length: 18; Block face height: 7; Block depth: 13; Cap length (0 for no caps): 18; Rows buried below ground: 1.
- Formula: Blocks = ⌈wall length ÷ block length⌉ × (⌈height ÷ block height⌉ + buried rows)
- Result: Wall blocks = 154 + 5–10% spare
- Rows: 7
- Blocks per row: 22
- Caps: 22
Things to keep in mind
- Follow your block manufacturer's instructions. Tall walls, slopes, driveways or buildings above the wall need engineering.
Questions people ask
How deep should the first row be?
Usually about 1/8 of the wall height, at least one block.
Do I need geogrid?
Often for walls over 3–4 ft; follow the manufacturer's design charts.