Retaining Wall Calculator — Blocks, Drainage & Base

It depends on block size. An 8×4×12 in block covers 0.67 sq ft of face area. Divide your total wall face area (length × height) by the block face area, then add 5–10% for waste and cuts.

Most jurisdictions require a permit for retaining walls taller than 3–4 feet (varies by location). Walls over 4 feet typically require an engineered design under the IRC and local codes. Always check with your local building department before starting.

Bury the first course of blocks at least 1 inch per 1 foot of wall height, with a minimum of 4–6 inches. In cold climates, the base should be below the frost line. A gravel base layer of 4–6 inches minimum is required for drainage and stability.

Drainage stone (typically #57 crushed stone) is packed behind the wall to allow water to drain rather than build up hydrostatic pressure. Without proper drainage, water pressure can push over a wall. Use at least 12 inches of drainage stone behind the blocks.

Properly built walls on a compacted gravel base settle very little — less than 1 inch. Wall failure usually comes from poor drainage behind the wall, an inadequate base, or building beyond the appropriate unreinforced height limit of 3–4 feet.