Retaining Wall Calculator
Calculate retaining wall blocks and materials by length and height. Free retaining wall calculator.
Planning a Retaining Wall
Walls under 3 feet can usually be built by a confident DIYer. Anything taller needs engineering — the lateral soil pressure increases exponentially with height, and a collapsed wall is dangerous and expensive to fix. Standard retaining wall blocks (like Allan Block or Versa-Lok) interlock without mortar. Each course steps back slightly, using gravity and friction to resist soil pressure. The base course is the most important — it must sit on 4-6 inches of compacted gravel, perfectly level. Get the base wrong and the whole wall leans within a year.
Drainage Behind the Wall
The number one cause of retaining wall failure is water pressure. Soil behind a wall absorbs rain like a sponge. Without drainage, that water pushes against the wall with enormous force. Every retaining wall needs: a perforated drain pipe at the base (wrapped in filter fabric), 12 inches of gravel backfill behind the blocks, and drain outlets at the ends. Skipping drainage to save $100-200 in materials guarantees premature wall failure that costs $2,000-5,000 to rebuild.
Allan Block, Versa-Lok, and Pavestone are the three most common retaining wall block brands. They are NOT interchangeable — each has a proprietary interlocking system. Choose one brand and stick with it for the entire wall. Mixing brands causes misalignment that worsens over time.
