Landscaping & hardscape
Retaining Wall Calculator
Estimate wall blocks, cap blocks, base gravel, drainage stone, drain pipe, waste, and optional block cost.
Estimated order quantity
0 blocks to buy
- Rows, blocks, and waste
- Base dimensions and rounding
- Drainage zone
- Caps, gravel, and wall blocks are separate quantities; geogrid is intentionally not estimated.
Planning estimate only. Verify product specifications, site conditions, and supplier purchase increments before ordering.
How the retaining wall estimate works
The calculator converts the exposed height into whole block rows, adds the selected buried courses, and rounds each row to whole blocks. It then applies a visible waste allowance. Caps are calculated separately from their face length.
Wall blocks: rows × round up(wall length ÷ block face length), then add waste and round up
Aggregate: length × width × depth ÷ 27, then add waste and round to the selected bulk increment
Base and drainage assumptions
The starting values use a 24-inch-wide, 6-inch-deep compacted aggregate base and a 12-inch drainage-stone zone behind the wall. CMHA guidance describes a leveling pad extending about 6 inches beyond the unit toe and heel and at least 6 inches thick, plus at least 12 inches of free-draining gravel behind segmental units. Replace these values with the selected wall system instructions and approved design.
Worked example
For a 40 ft wall with 40 inches exposed, 8-inch-high × 16-inch-long blocks, one buried course and 10% waste, the estimate is 6 rows, 30 blocks per row, and 198 wall blocks. With 16-inch caps, buy 33 caps. A 24 × 6 in base and a 12 in drainage zone, rounded to 0.5 yd³ increments, require about 2.0 yd³ of base gravel and 6.0 yd³ of drainage stone including the same allowance.
Engineering and site limits
This is a purchase-planning tool, not a wall design. Do not derive geogrid type, length, layer spacing, connection strength, or embedment from a generic formula. Soil, groundwater, slopes, tiered walls, seismic conditions, wall batter, block system and loads from driveways, buildings or fences materially affect stability. Obtain the manufacturer’s system design and a qualified local engineer when required; check permits and call 811 before excavation.
Technical references: CMHA Segmental Retaining Wall Installation Guide, CMHA Segmental Retaining Wall Design, CMHA 2025 sample specifications, and Lowe’s block retaining wall planning guide. Product instructions and the project design control.
Retaining wall calculator FAQ
Does the exposed height include the buried course?
No. Enter the visible height and select the number of additional buried courses separately.
Why are caps separate from wall blocks?
Caps form the top finish and may have a different face length, packaging, cuts and adhesive requirements.
Does the drainage-stone estimate include hollow block cores?
No. Core volume is product-specific; add the manufacturer’s stated core-fill quantity.
Does this calculate geogrid?
No. Geogrid is a structural system component that requires product-specific and site-specific design.