Standard retaining-wall blocks are often 12 in wide × 6 in high.
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.
Project dimensions
Wall lengthft
Wall heightft
Block widthin
Block heightin
Updates automatically as you change measurements.
Estimated materials
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
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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