Calculate blocks, base gravel, and backfill for your retaining wall project — free and easy.
How to Use This Retaining Wall Calculator
Enter your wall length and height in feet. Select your block size — standard 6×16 blocks require about 1.5 per square foot of wall face; larger blocks fewer. The calculator includes a 10% waste factor for cuts. Results show blocks needed plus base gravel and backfill estimates.
Building a Retaining Wall That Lasts
Three things wreck retaining walls: poor drainage, insufficient base, and inadequate embedment. Getting these right at the start is the difference between a wall that lasts 50 years and one that bulges after two winters.
Critical Design Elements
- Base trench: 6 inches of compacted gravel below the first course of blocks. The trench should be 12-18 inches wide (twice the block depth). The first course must be perfectly level — every block above it depends on this.
- Embedment: Bury the first course below grade. For walls under 4 feet, bury 1 inch per foot of wall height (minimum 6 inches). For walls over 4 feet, get an engineer — most jurisdictions require a permit and stamped plans.
- Backfill drainage: 12-18 inches of clean crushed stone directly behind the wall, with a perforated drain pipe at the base to carry water away. Never backfill with the soil you excavated — it holds water and creates hydrostatic pressure.
- Batter (setback): Retaining wall blocks typically have a built-in lip that sets each course back about 3/4 inch. This slight tilt into the hillside is critical for stability.
For walls over 3-4 feet, consider using geogrid reinforcement — synthetic mesh that ties the wall back into the soil mass behind it. The cost is modest ($0.50-1.00 per sq ft) and dramatically increases holding capacity.