Retaining Wall Calculator — Blocks, Gravel & Materials Estimate
Estimate how many wall blocks, cap blocks, gravel, filter fabric, and adhesive tubes you need for your retaining wall.
How to Use This Calculator
- Enter the total length of your retaining wall in feet.
- Enter the exposed wall height in feet (do not exceed 6ft without an engineer).
- Select your block type (standard or large segmental block).
- Toggle whether you plan to use cap blocks and drainage gravel.
- Adjust the waste factor if needed and click "Calculate".
How the Calculation Works
wall_height_in = wall_height_ft × 12
wall_length_in = wall_length_ft × 12
rows = ceil(wall_height_in / block_height)
blocks_per_row = ceil(wall_length_in / block_length)
total_wall_blocks = rows × blocks_per_row × (1 + waste)
cap_blocks = cap_enabled ? blocks_per_row : 0
gravel_cubic_yards = (wall_length_ft × 1 × wall_height_ft) / 27
filter_fabric_sqft = wall_length_ft × (wall_height_ft + 2)
adhesive_tubes = ceil(wall_length_ft / 20) The calculator estimates block rows based on wall height and block dimensions, then multiplies by blocks per row and a waste factor. It also estimates drainage gravel volume, filter fabric area, and construction adhesive tubes based on wall length and height.
Variables:
- wall_length_ft: Total length of the retaining wall in feet
- wall_height_ft: Exposed wall height in feet (do not exceed 6ft without engineering)
- block_height: Height of a single block in inches
- block_length: Length of a single block in inches
- waste: Extra percentage of blocks for cuts, breakage, and waste
Pro Tips
- Always dig down to undisturbed soil and build a compacted gravel base beneath the first course.
- Bury at least the bottom course (or more) below grade for stability.
- Use drainage gravel and a drain pipe behind the wall to relieve hydrostatic pressure.
- Step taller walls back slightly and never exceed local code height without an engineered design.
Recommended Retaining Wall Tools
Landscape Block Adhesive
Adheres cap blocks and units for a solid wall.
View on Amazon →Filter Fabric / Landscape Fabric
Separates soil from drainage gravel behind the wall.
View on Amazon →Drainage Gravel
Clean, free‑draining gravel for backfill.
View on Amazon →Plate Compactor (rental)
Compact the base and backfill for a long‑lasting wall.
View on Amazon →Dead Blow Mallet
Tap blocks into alignment without damaging them.
View on Amazon →String Line and Stakes
Keep your wall straight and level during layout.
View on Amazon →Frequently Asked Questions
How deep should the base be for a retaining wall?
A typical small retaining wall uses 4–6 inches of compacted gravel base below the first course, plus at least one buried course. Always follow manufacturer and code guidelines.
Do I need drainage behind a retaining wall?
Yes. Most retaining walls need drainage gravel and a perforated drain pipe behind the wall to relieve hydrostatic pressure and prevent failure.
How tall can a DIY retaining wall be?
Many jurisdictions limit unengineered segmental retaining walls to about 3–4 feet. Walls over 4 feet typically require an engineer’s design and permits.
Should I glue the cap blocks?
Yes, cap blocks are usually adhered with landscape block adhesive to prevent movement and create a finished look.