Standard retaining-wall blocks are often 12 in wide × 6 in high.
MEASURE. ESTIMATE. BUILD.
Retaining Wall Calculator
Enter your wall length and height plus the block dimensions to get the number of blocks, the course count, and the volume of base gravel needed.
01 / PROJECT DIMENSIONS↙
Wall lengthft
Wall heightft
Block widthin
Block heightin
Change any measurement to update your estimate.
02 / YOUR MATERIAL ESTIMATE
You need approximately
120 blocks
6 courses × 20 per course
- Wall face area
- 60 ft²
- Courses
- 6
- Base gravel
- 0.74 yd³
Field notes
The base course is the whole wall — spend your time leveling the gravel pad, because every course above copies its errors. Bury the first course at least one block-height below grade so the wall can't kick out at the bottom. The calculator sizes a base one block wider than the wall and 6 inches deep for exactly this reason. Anything over 3–4 feet usually needs an engineer and a permit; check locally before you dig.
How the retaining wall calculator works
The math behind the tool:
blocks = (wall length ÷ block width) × (wall height ÷ block height)Sources: Concrete Masonry & Hardscapes Association (segmental retaining wall installation (formerly ICPI/NCMA)).
Frequently asked questions
How many retaining wall blocks do I need?
Divide the wall length by the block width and the wall height by the block height, then multiply the two. A 20 ft long, 3 ft high wall with 12×6 in blocks needs about 120 blocks.
How much base gravel goes under a retaining wall?
Plan on a compacted gravel base about 6 inches deep and one block-width wider than the wall; the calculator returns this base volume in cubic yards.
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