Retaining Wall Block & Gravel Calculator
Calculate total interlocking retaining wall blocks, crushed gravel backfill tons, drainage pipe length, and leveling base sand for garden and landscape retaining walls.
Calculated Results
Frequently Asked Questions
How high can you build a DIY retaining wall without an engineer?
In most US jurisdictions and building codes (IBC/IRC), retaining walls up to 4 feet tall (measured from bottom of footing to top of wall) can be built without an engineer's stamped drawings. Walls over 4 feet, or walls supporting sloped driveways, require structural engineering and geogrid soil reinforcement.
Why is gravel backfill essential behind a retaining wall?
Hydrostatic pressure from trapped water is the #1 cause of retaining wall failure. A continuous 12-inch wide vertical layer of clean angular crushed stone (3/4" clear gravel) behind the blocks allows water to quickly percolate down to a perforated drain pipe rather than pushing against the blocks.
How deep should the first course of retaining blocks be buried?
A minimum of one full block height or 6 inches of the base course must be buried below finished grade for walls up to 3 feet. Taller walls require burying 1 inch of block for every 8 inches of wall height to resist lateral sliding forces.
Do retaining walls need landscape fabric?
Yes. Landscape filter fabric should be placed between the gravel drainage backfill and the native soil embankment to prevent fine dirt and clay particles from silting up the drainage gravel and clogging the perforated pipe.