By Zencalcy Editorial TeamLast reviewed About us
A block retaining wall is measured by face area: standard 8 × 16 inch blocks cover 0.888 square feet each. Behind the face you also need a compacted base, a gravel drainage column and perforated pipe, which is where most of the labour hides.
Blocks, caps, base and backfill for a block retaining wall.
Blocks = ⌈L × H ÷ 0.888⌉ Caps = ⌈L ÷ 1.33⌉ Base = L × 1.5 ft × 0.5 ft
The 0.888 sq ft face is an 8 × 16 inch block. Add 5% for cuts and breakage, and do not count the buried course: walls over 2 ft tall usually bury the first course for stability. Base assumes a 12 inch wide, 6 inch deep compacted trench.
| Symbol | Meaning |
|---|---|
| L | Wall length in feet. |
| H | Finished height in feet. |
| N | Blocks needed. |
60 sq ft ÷ 0.888 = 68 blocks, plus 5% = 72. Cap units are 16, base gravel about 1.67 cu yd.
Continue with the Gravel Calculator, Sand Calculator, Rock Calculator, or the River Rock Calculator — or browse more materials & quantities and all construction calculators.
Most codes allow segmental block walls up to 4 ft without engineering, provided the base and drainage are right. Above that, and for surcharge loads, get a design.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026