Retaining Wall Calculator
Enter the wall's length and height and your block's face size, and this gives the number of retaining-wall blocks and courses — the materials count, not the engineering.
Wall blocks
99blocks
- Rows (courses)
- 5 rows
- Wall face area
- 60 sq ft
This estimates wall block and course counts only — NOT a structural design. Base preparation, drainage gravel, backfill, geogrid reinforcement, and batter are project-specific, and retaining walls above ~3–4 ft (or holding back a slope, driveway, or structure) typically require an engineer and a permit. Follow the block manufacturer's specs and local code.
How it’s calculated
Blocks = wall face area × blocks per square foot × (1 + waste), rounded up. Wall face area is length × height; blocks per square foot is 144 ÷ (block face width × height in inches). Courses (rows) = wall height ÷ block face height. Enter the full height including the base course(s) below grade (typically the bottom 10–15%), or you'll order short.
Worked example
A 20 ft × 3 ft wall = 60 sq ft. A 12 × 8-inch block face is 96 sq in → 144 ÷ 96 = 1.5 blocks/sq ft. 60 × 1.5 × 1.10 (10% waste) ≈ 99 blocks, in ⌈36 ÷ 8⌉ = 5 courses (plus a cap row).
FAQs
- What size are retaining-wall blocks?
- They vary widely — segmental (SRW) units range from small 4 × 12-inch-face pavers to large 8 × 18-inch units, and many are wedge-shaped for curves. Read the face dimensions off your block (or its spec sheet) and enter them.
- Do I need cap blocks?
- Usually yes — a finishing row of cap blocks tops the wall, often glued on with masonry adhesive. Add that row's length to your order; this count covers the wall body.
- How tall can I build without an engineer?
- It depends on local code, soil, and what's behind the wall, but many jurisdictions require an engineered design and a permit above about 3–4 feet, or for any wall holding up a slope, driveway, or structure. Check before you build.
Sources
- Blocks = wall area × (144 ÷ block-face area in²) × (1 + waste), rounded up. Geometry only — block face dimensions are product-specific (enter your unit's).