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Calculate blocks, gravel, and materials for retaining walls
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A retaining wall block calculator helps you determine the exact number of blocks, gravel, drainage materials, and accessories needed to build a retaining wall. These walls hold back soil on slopes or create level terraces in your landscape.
This calculator accounts for:
Example: 20 ft wall ÷ 12" blocks = 240" ÷ 12 = 20 blocks per course
Example: 24" wall ÷ 4" block height = 6 courses
Example: 20 × 6 = 120 blocks × 1.10 (10% waste) = 132 blocks
| Block Type | Size (L×H×D) | Weight | Best For |
|---|---|---|---|
| Standard Block | 12×4×8" | 35 lbs | DIY walls, small projects |
| Large Block | 16×6×12" | 60 lbs | Taller walls, faster coverage |
| Split Face | 12×4×8" | 38 lbs | Natural stone look |
| Tumbled Block | 12×4×10" | 40 lbs | Aged/rustic appearance |
| Garden Wall | 12×4×6" | 28 lbs | Borders, short walls |
| Allan Block (AB) | 18×8×12" | 75 lbs | Commercial, engineered walls |
Excavate 4-6 inches below grade. Install compacted gravel base that extends 3-6 inches beyond the block on each side. The base should be level and extend 1 inch below the first course of blocks.
Install perforated drain pipe at the base behind the wall. Backfill with drainage gravel (not soil) for the full height. Use landscape fabric to prevent soil from clogging the gravel.
Offset each course by half a block length (running bond pattern). Use block adhesive between the top 2-3 courses and all cap blocks. Fill hollow cores with gravel for added stability.
Most blocks have a built-in setback (3/4" per course) that leans the wall into the slope. This increases stability and load capacity significantly.
Important: Local building codes vary. Walls over 4 feet typically require permits and engineered designs. Always check with your local building department before starting.
For standard 12×4" blocks, you need approximately 3 blocks per square foot of wall face. Larger 16×6" blocks require about 1.5 blocks per square foot.
Yes, the first course should be buried about 1 inch below grade. This provides stability and prevents the wall from sliding forward under pressure.
Fill the space behind the blocks with 12 inches of drainage gravel for the full height of the wall. Use clean, crushed stone (3/4" minus) that drains well.
Adhesive is required for cap blocks and recommended for the top 2-3 courses. Lower courses rely on weight and setback for stability. Use construction adhesive rated for masonry.
Yes, but "step" the base to follow the slope. Each step should be the height of one block. The bottom of each section needs its own compacted gravel base.
For curves, use smaller blocks or cut standard blocks at angles. Add 15% extra blocks for waste. Tight curves may require cutting each block.