Calculators/ Masonry & Aggregate/Retaining Wall Calculator
Retaining Wall Calculator
Blocks, base gravel and drainage for a retaining wall.
Retaining Wall Calculator
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Retaining walls fail from water, not from weight. The block count is the easy part; the compacted base and the drainage stone behind the wall are what keep it standing.
How this is calculated
- Courses = wall height ÷ block height. Blocks per course = wall length ÷ block length.
- The base trench is typically 12 inches wide and 6 inches deep, compacted, with the first course buried.
- Allow a foot of clean drainage stone behind the full height of the wall, with a perforated pipe at the base.
Frequently asked questions
How high can I build without an engineer?
Four feet is the common limit in US residential code before an engineered design is required. Check locally: some jurisdictions set it at three.
Do I need geogrid?
Generally above three to four feet, or wherever there is a surcharge load such as a driveway or slope above the wall.