Retaining Wall Calculator
Your estimate
- Blocks per course
- 23
- Cap blocks
- 23
- Drainage gravel
- 3.89 yd³105 ft³ · 2.97 m³
- Gravel weight
- 5.24 tons10,488 lb · 4.76 t
For segmental retaining wall blocks — counts the buried course, caps and the gravel behind the wall.
Updated 2026-10-20 · Based on: standard block, brick and paver sizes with their mortar joints.
How to use the Retaining Wall Calculator
- Enter the wall length and the height above ground.
- Choose the block face size.
- Keep “bury first course” on (most makers require it).
- Read blocks, caps and gravel.
Formula
Courses = height ÷ block height (+1 buried). Blocks per course = length ÷ block length.
Drainage gravel = length × wall height × backfill width (usually 12 in).
Worked example
With the values preset in the calculator above:
- Length
- 30 ft
- Height
- 3 ft
- Wall block
- 16 × 6 in face
- Bury first course
- Yes
- Gravel backfill width
- 12 in
- Extra for waste
- 5 %
- Wall blocks (with waste)
- 170
- Courses (rows)
- 7
- Blocks per course
- 23
- Cap blocks
- 23
- Drainage gravel
- 3.89 yd³ (105 ft³)
Frequently asked questions
How many blocks for a 30 ft retaining wall 3 ft high?
With 16 × 6 in blocks: 7 courses of 23 blocks — 170 blocks with 5 % extra, plus 23 caps.
How tall can a block retaining wall be without an engineer?
Many codes allow about 4 ft (1.2 m) without engineering. Taller walls or walls holding a slope or driveway usually need geogrid and a design.
Why bury the first course?
It keeps the base from sliding out — most block makers ask for about 1 in buried per 8 in of wall height, at least one full course.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.