Retaining Wall Calculator
Estimate retaining wall blocks and base gravel by wall length and height.
Blocks needed
66 blocks
- Courses
- 4
- Blocks per course
- 15
- Base gravel (est.)
- 0.49 cu yd
How we calculate this
Courses = wall height ÷ block height. Blocks per course = wall length ÷ block length. Total blocks = courses × blocks per course, plus a waste allowance for cuts and corners.
Example
Measuring tips
Measure the total length of wall needed and the maximum height at the tallest point. Most segmental retaining wall blocks are 6 inches tall and 16-18 inches long — check your specific product's dimensions for an exact count.
Common mistakes
- Skipping proper base gravel and compaction, which causes walls to settle or lean over time.
- Not accounting for wall batter (slight backward lean), which adds coverage per course.
- Ignoring drainage behind the wall — a lack of gravel backfill is a leading cause of failure.
Frequently asked questions
How many blocks do I need for a 4ft retaining wall?
With standard 6in-tall blocks, a 4ft wall needs 8 courses. Multiply by your wall length divided by block length to get total blocks per course.
Do retaining walls need a gravel base?
Yes — a compacted gravel base (typically 6 inches) under the full footprint is standard for drainage and stability, even on short walls.
Related calculators
Estimates are provided for planning purposes. Actual material requirements may vary based on supplier specifications, compaction, site conditions, installation method, waste, and local code.