Retaining Wall Calculator — blocks, base and drainage

Block count, buried base course and drainage stone for a retaining wall, with the height at which engineering and permits enter the picture.

Retaining Wall Calculator — blocks, base and drainage

Block count is easy arithmetic. Retaining walls fail from water and from a bad base, not from a miscount, so the base course and the drainage stone are in here too.

Units

Wall length (ft)

Exposed wall height (ft)

Block face length (in)

Block height (in)

Block depth (in)

Buried base courses

Drainage stone behind wall (in)

Waste

The first course goes below grade and sits on compacted stone. Water behind the wall is what pushes it over, so the drainage layer is structure, not an extra.

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Courses (exposed + buried)	—
Blocks per course	—
Blocks total	—
Wall face area	—
Base stone	—
Drainage stone	—
Backfill behind wall	—

Blocks per course is wall length ÷ block face length, and total courses is the exposed height plus the buried ones. A common rule of thumb buries the first course, or about a tenth of the wall height, and sets it on 6″ of compacted crushed stone.

Drainage stone is estimated as a vertical strip the depth you set, running the full height and length behind the wall. Wall height is the one number that changes the whole job: past roughly 4 ft most jurisdictions require an engineered design and a permit, and geogrid reinforcement usually enters the picture well before that. Soil type, slope above the wall and any surcharge — a driveway, a pool, a structure — all change what is required. Check with your building department before building anything that retains soil.