Face-area method
Courses = ceil(wall height ÷ block height). Blocks per course = ceil(wall length ÷ block length). Total = courses × blocks per course, then add waste. Default face size is 18" × 6", a common segmental block module—override with your block’s actual face dimensions.
Worked example
For a 20 ft long, 3 ft high wall with 18×6 inch blocks: courses = 6; blocks/course = ceil(20 ÷ 1.5) = 14; total = 84 blocks before waste. Base trench gravel is estimated from length × base width × base depth.
Drainage matters
Segmental walls usually need free-draining backfill and outlet pipes. Do not backfill with heavy clay against the blocks. Use the gravel calculator for larger drain-rock volumes.
Common mistakes
- Skipping compacted base leveling pads.
- Ignoring setback/batter requirements per course.
- Using landscape wall blocks beyond their rated height.
| Block face | Blocks / sq ft |
|---|---|
| 16×6 in | ~1.5 |
| 18×8 in | ~1.0 |
| 12×4 in | ~3.0 |
Assumptions and limits
The retaining wall calculator results are planning estimates for rectangular or cylindrical shapes with uniform depth. Real sites have slopes, voids, and product variation. Always confirm coverage with the manufacturer label and local building practices before you buy large quantities.
Unit toggles switch input labels between US imperial and metric. Shareable URLs store your inputs in the query string for convenience, while the canonical tag stays on the clean page URL so search engines do not index every parameter combination.
Shopping checklist
- Write down the calculator outputs (volume, bags, or piece counts) and round up for waste.
- Call your supplier for density, dye lot, or delivery minimums when ordering bulk material.
- Check access for trucks, wheelbarrows, and staging space before delivery day.
- Photograph existing conditions so you can revisit dimensions if a helper measures differently.
Stake the wall alignment and check the first course with a level; block counts assume a level base trench.
FAQ
Do I need geogrid?
Taller walls and surcharged slopes often require engineering and geogrid. Follow the block manufacturer’s height limits and local code.
Related guides
Sources
- NCMA – Segmental retaining walls Used for: SRW block and base practice overview; height limits are manufacturer-specific. Checked .
Estimates only—confirm bag yields on the product label and check local building codes before you pour or order. Not affiliated with QUIKRETE, Sakrete, Sonoco, or any manufacturer named in the sources. Found an error? Tell me.
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