Construction • Material Estimator

Retaining Wall Block Calculator

Calculate blocks, caps, buried base courses, leveling gravel, and drainage rock for segmental and garden retaining walls

Measurement Units:
Waste Buffer:

1. Wall Dimensions

ft
ft
Embedding the first course prevents toe kickout.
inches
6" compacted aggregate is standard.

2. Estimated Material Costs

Total Retaining Blocks
203
23 blocks per course × 8 total courses (10% buffer)
$1,239 Est.
6.1 tons total gravel
Total Wall Height
8 courses
7 exposed + 1 buried below grade
Cap Stones & Adhesive
33 caps
2 tubes landscape block adhesive
Leveling Trench Gravel Base
1.43 tons
Compacted 3/4" minus / crusher run base
Drainage Backfill Gravel
4.67 tons
12" drainage chimney behind wall
Drain Pipe & Geotextile
40 ft drain pipe
220 sq ft filter fabric wrap
Total Gravel Volume
4.35 cu yd
117 cubic feet of stone
Retaining Wall Cross-SectionSide Elevation View
Retained Soil12" Gravel DrainageCompacted Gravel Base (6")Ground LineBuried Row

How to Build a Long-Lasting Retaining Wall

1. Solid Compacted Foundation

Never build on bare dirt or uncompacted ground. Excavate a trench at least 18"–24" wide, add 6" of 3/4" minus crushed stone with rock dust, and tamp with a mechanical plate compactor.

2. Always Bury the Base Row

Bury at least 1 full block course (minimum 6" deep) below ground level. This anchors the toe of the wall and prevents the foundation from sliding outward under soil pressure.

3. Unhindered Water Drainage

Water is the #1 cause of retaining wall collapses. Backfill a 12" gravel chimney directly behind the blocks and place a perforated 4" corrugated drainage pipe wrapped in filter fabric at the bottom.

Frequently Asked Questions (FAQ)

Burying the first course at least 6 inches (one full block height) below grade anchors the toe of the wall into the earth. This passive resistance prevents hydrostatic soil pressure from sliding or kicking out the bottom rows of blocks.

Yes. Trapped water is the primary cause of retaining wall blowouts. A minimum 12-inch wide vertical drainage column of 3/4" angular clean crushed stone placed immediately behind the blocks, coupled with a perforated 4-inch drain pipe wrapped in geotextile fabric draining to daylight, relieves hydrostatic build-up.

Most local building codes require engineered geogrid reinforcement mesh for any segmental retaining wall 4 feet (1.2 meters) or higher, or any height if supporting a surcharge load (such as a driveway, patio, or sloping hillside). Geogrid locks the blocks to the retained soil mass behind them.

First, calculate total wall height including the buried base course. Divide wall length (in inches) by block length (e.g. 12" or 18") to get blocks per row. Divide total height by block height (e.g. 6" or 8") to get row count. Multiply rows by blocks per row, and add 5–10% extra for cutting ends and steps.

Dry-stacked segmental retaining wall (SRW) blocks (such as Allan Block, Belgard, or Keystone) do NOT use wet mortar; they interlock using built-in rear alignment lips, pins, or setback flanges. However, the top cap stones and top two block courses should be permanently glued using exterior polyurethane masonry adhesive.