Retaining Wall Block Calculator
* Materials only. Does not include excavation, drainage, or labor ($15–$40/sq ft). Walls over 4 ft require engineering. Add 5–10% for waste.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Retaining Wall Block Pricing
| Block Type | Dimensions | Price / Block |
|---|---|---|
| Standard Block | 8" × 6" × 16" | $2 – $4 |
| Large Block | 12" × 8" × 18" | $5 – $8 |
| Allan Block | 12" × 8" × 12" | $3.50 – $6 |
| Versa-Lok | 12" × 6" × 16" | $4 – $7 |
Blocks Needed by Wall Size (Standard 16\" Blocks)
| Wall Size | Blocks Needed | Material Cost |
|---|---|---|
| 10 ft × 2 ft | 30 blocks | $60 – $120 |
| 20 ft × 3 ft | 90 blocks | $180 – $360 |
| 30 ft × 3 ft | 135 blocks | $270 – $540 |
| 40 ft × 4 ft | 240 blocks | $480 – $960 |
* Materials only. Add $150–$400 for base gravel, $100–$300 for backfill, and $15–$40/sq ft for labor.
How We Calculate
Our retaining wall block calculator estimates blocks needed based on wall length, height, and block dimensions. Calculations include rows per height and blocks per length to determine total quantity.
How the math works: Blocks per row = wall length (inches) ÷ block width. Rows needed = wall height (inches) ÷ block height. Total blocks = blocks per row × rows. Round up to nearest whole block. Add 5–10% for waste and cuts.
Block Type Comparison
Standard Blocks (8×6×16", $2–$4 each) are basic concrete blocks for low walls (1–3 ft). Widely available at Home Depot and Lowe's. Limited color options. Good for budget projects and utility walls.
Large Blocks (12×8×18", $5–$8 each) are heavy-duty for taller walls (3–6 ft). Fewer blocks needed, faster installation. Better stability with deeper 12" footprint. Used for commercial and high-load applications.
Allan Block (12×8×12", $3.50–$6 each) features hollow-core design with pinning system. Lightweight for DIY installation. Great for curves and terracing. 50+ color options. Popular for residential landscaping.
Versa-Lok (12×6×16", $4–$7 each) uses solid concrete with mechanical interlock. No pins needed. Strongest option for tall walls (4–8 ft). Commercial grade. Requires geogrid reinforcement for walls over 4 ft.
Base and Cap Requirements
Gravel Base: Excavate 6–8" below grade. Fill with ¾" crushed gravel. Compact in lifts with plate compactor ($75/day rental). Level to within ¼" across wall length. Gravel costs $30–$50/ton delivered (need 1–2 tons for typical wall).
Cap Blocks: Flat-top blocks for finished appearance and water protection. Cost $8–$15 each or $5–$10 per linear foot of wall. Secure with concrete adhesive ($6/tube, need 1 tube per 10 ft). Optional but recommended for all exposed walls.
Additional Materials
Our estimates cover blocks only. Not included: excavation ($200–$800 depending on wall size), backfill gravel (12–18" behind wall, $150–$400), perforated drain pipe ($1–$2/ft), landscape fabric ($0.20/sq ft), geogrid ($2–$3/sq ft for walls over 4 ft), and labor ($15–$40/sq ft for professional installation).
Data Sources
Block pricing from Home Depot, Lowe's, Allan Block, Versa-Lok, and Keystone manufacturers. Installation data from contractor estimates and manufacturer guidelines. We review and update regularly.
Last updated: 2026-02-09
Frequently Asked Questions
How many blocks do I need for a retaining wall? +
Formula: (Wall length ÷ block width) × (wall height ÷ block height). For a 20-ft × 3-ft wall with standard 16" blocks: (240" ÷ 16") × (36" ÷ 6") = 15 blocks per row × 6 rows = 90 blocks. Add 5–10% for waste and cuts. Block dimensions vary by brand (Allan Block, Versa-Lok, Keystone).
How much do retaining wall blocks cost? +
Retaining wall blocks cost $2–$8 per block depending on size and brand. Standard 8×6×16" blocks cost $2–$4 each. Large 12×8×18" blocks cost $5–$8. Allan Block runs $3.50–$6, Versa-Lok $4–$7, Keystone $3–$5. Cap blocks cost $8–$15 each. Materials for a 20-ft × 3-ft wall: $180–$720.
What size block for 3-foot retaining wall? +
Standard 8×6×16" or 12×8×18" blocks work for 3-ft walls. Use 6" height blocks for 6 rows, or 8" blocks for 4–5 rows. Versa-Lok and Allan Block 12" depth blocks provide better stability for 3+ ft walls. Walls over 4 ft require engineering and geogrid reinforcement per most building codes.
Do I need a gravel base for retaining wall blocks? +
Yes, gravel base is required for all retaining walls. Excavate 6–8" below grade and fill with crushed ¾" gravel. Compact in 2–3" lifts with plate compactor. Level gravel base ensures first course is level — critical for entire wall. Gravel also provides drainage behind wall. Costs $50–$150 for typical residential wall base.
Can I build a retaining wall without cap blocks? +
Technically yes, but cap blocks are recommended. Caps protect wall top from water infiltration, provide finished appearance, and add weight for stability. Cap blocks cost $8–$15 each or $5–$10 per linear foot. Skip caps only for temporary walls, utility areas, or budget constraints. Use construction adhesive to secure caps.
How high can I build a block retaining wall? +
DIY limit is 3–4 ft without engineering. Most residential codes allow 4 ft max without engineer stamp and permit. Walls 4–8 ft require geogrid reinforcement (fabric layers every 2–3 courses). Walls over 8 ft need engineered design, concrete footing, and professional installation. Check local building codes before starting.
What is the difference between Allan Block and Versa-Lok? +
Allan Block uses hollow-core concrete blocks with pinning system. Lightweight, easy DIY installation, good for curves. $3.50–$6/block. Versa-Lok uses solid concrete units with mechanical interlock. Heavier, stronger, better for tall walls and commercial use. $4–$7/block. Both require gravel base and proper backfill. Choose based on wall height and complexity.
Do I need drainage behind a retaining wall? +
Yes, drainage is critical. Hydrostatic pressure from saturated soil causes wall failure. Install 4" perforated drain pipe at base of wall in gravel trench. Backfill with 12–18" crushed gravel behind wall. Run drain pipe to daylight or dry well. Use landscape fabric between gravel and soil. Proper drainage doubles wall lifespan.
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