Retaining Wall Calculator

How to Estimate a Retaining Wall

Segmental retaining walls (SRW) use interlocking concrete blocks that stack without mortar. The block count is determined by wall face area divided by the block face area. But blocks are only part of the materials list — you also need base gravel for the foundation trench, drainage gravel behind the wall, cap blocks on top, and landscape adhesive to secure the cap course.

Height Limitations

Most segmental retaining walls under 4 feet in exposed height can be built without engineering or geogrid reinforcement — but always check your local building code. Walls over 4 feet typically require a building permit, engineered drawings, and geogrid reinforcement layers between courses. The National Concrete Masonry Association (NCMA) publishes design standards for SRW construction.

The Bottom Line

A retaining wall is part structure, part drainage system. The blocks are the visible part, but the gravel base and drainage backfill are what keep it standing. Skimp on the base and the wall settles. Skip the drainage gravel and water pressure pushes it over. This calculator estimates all the materials — blocks, caps, base gravel, backfill, and adhesive — from your wall dimensions. For walls over 4 feet, consult an engineer before ordering materials.