Retaining Wall Calculator
Calculate how many blocks you need for your retaining wall. Get block count, base gravel, backfill, and cost estimates.
Last updated: January 13, 2026
Enter Your Wall Dimensions
Small raised bed, 1-2 ft high
ft
ft
Height:
Most common size, easy to handle
Easy DIY, no mortar needed · $3-10/block
%
Include cap blocks (top row)
Include base materials
6" base and 12" backfill recommended for most walls
Enable cost estimate
Results
132
blocks needed
(includes 10% waste)
Wall Size:20 ft × 2.0 ft
Wall Area:40 sq ft
Columns × Rows:20 × 6
Blocks (no waste):120
Extra for waste:+12
Cap Blocks:20
Base Materials:
Base Gravel (6"):0.52 cu yd
Backfill (12"):1.63 cu yd
Total Gravel:2.15 cu yd (3.01 tons)
Calculation Steps
Wall Length: 20 ft= 20 ft
Wall Height: 2 ft= 2.0 ft
Columns: 20 ft × 12 ÷ 12"= 20
Rows: Height ÷ 4"= 6
Blocks (no waste): 20 × 6= 120
+ 10% waste: 120 × 1.10= 132
Cap Blocks: 20 columns= 20
Total Gravel: Base + Backfill= 2.15 cu yd
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How to Use This Calculator
- Select your project type — Garden bed, terraced landscape, or hillside retention.
- Enter wall dimensions — Measure the total length and desired height of your wall.
- Choose block size and type — Standard 12" × 4" blocks are most common for DIY projects.
- Include base materials — Toggle on to calculate gravel for base and backfill drainage.
- Review results — See block count, cap blocks, gravel needed, and cost estimate.
How We Calculate
Blocks = (Wall Length ÷ Block Width) × (Wall Height ÷ Block Height) × (1 + Waste%)
Example: 20 ft × 2 ft Wall with Standard Blocks
- • Columns: 20 ft × 12 ÷ 12" = 20 columns
- • Rows: 2 ft × 12 ÷ 4" = 6 rows
- • Blocks needed: 20 × 6 = 120 blocks
- • With 10% waste: 120 × 1.10 = 132 blocks
- • Cap blocks: 20 blocks (one per column)
Common Block Sizes:
- • Standard: 12" × 4" × 7" (most common)
- • Large: 18" × 6" × 12" (fewer blocks needed)
- • Small: 8" × 4" × 6" (good for curves)
Base Material Guidelines:
- • Base gravel: 6" deep, 2× block depth wide
- • Backfill: 12" behind wall for drainage
- • Add 20% to base gravel for compaction
- • Add 10% to backfill for voids
Based on ICPI (Interlocking Concrete Pavement Institute) and Lowe's installation guidelines.