Retaining Wall Calculator — Blocks, Base & Drainage
Who this is for: For landscapers and DIYers planning a segmental block wall — the block order, the base gravel nobody budgets, and the drain pipe that keeps the wall from failing.
Wall length and height in — block count for your block size, cap blocks, base gravel tons, and drain pipe length out. Segmental block walls.
Quick answer: Blocks = wall face area ÷ block face area × 1.05. A 30-ft × 3-ft wall with 16×8 blocks ≈ 107 blocks + 23 caps, ~1.4 tons of base gravel, and 30 ft of drain pipe.
36 in ≈ the 3-ft DIY line
16 in standard
8 in standard
| Standard block | 16 × 8 in face = 0.889 sf |
|---|---|
| Per sf | 1.125 blocks (×1.05 cut allowance) |
| Base | 6 in compacted gravel, block width + 6 in |
| Gravel weight | ≈1.35 tons per yd³ |
How does the retaining wall calculator work?
Blocks are wall face area ÷ block face area: a standard 16 × 8-inch face block covers 0.889 sf, so a 30-foot wall 3 feet high (90 sf) takes about 107 blocks with a 5% cut allowance. The cap course runs one cap block per block width along the top. The base is where estimates blow up: a compacted gravel trench — wall length × (block depth + 6 inches) wide × 6 inches deep — runs about 0.05 tons of gravel per foot for a 16-inch block, and skimping on compaction is the number-one wall failure. Drain pipe runs the full length behind the wall with daylight or a pop-off; the calculator sizes all of it from your block dimensions.
Common uses
- Ordering blocks for a garden or terraced wall
- Budgeting base gravel that quotes always forget
- Sizing drain pipe runs behind the wall
- Checking a landscaper's block count against your own