Retaining Wall Calculator
Calculate how many retaining wall blocks you need, number of courses, cap blocks, backfill gravel, and drainage materials for any wall size.
ft
ft
Total Blocks (5% waste)
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Number of Courses —
Cap Blocks Needed —
Extended More scenarios, charts & detailed breakdown ▾
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ft
%
Wall Blocks
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Courses —
Cap Blocks —
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ft
in
in
in
$
$
Block Counts
Number of Courses —
Total Blocks —
Cap Blocks —
Base & Drainage
Base Gravel (yd³) —
Drainage Gravel (yd³) —
Filter Fabric (sq ft) —
Engineering
Geogrid Reinforcement —
Batter Angle —
Cost Estimate
Block Material Cost —
Total Material Cost —
How to Use This Calculator
- Enter the wall length and height in feet.
- Select your block size.
- Results show total blocks, number of courses, and cap blocks needed.
Formula
Courses = Wall Height (in) ÷ Block Height (in)
Blocks per course = Wall Length (ft) × 12 ÷ Block Length (in)
Total blocks = Courses × Blocks per course × 1.05 (waste)
Example
Example: 20 ft long × 3 ft high wall with 6×16 in blocks → 6 courses × 15 blocks = 90 blocks + 5% waste = 95 blocks.
Frequently Asked Questions
- Divide wall length by block length to get blocks per course. Divide wall height by block height to get number of courses. Multiply to get total blocks, then add 5–10% for waste.
- Walls taller than 4 feet typically require geogrid reinforcement layers every 2–3 courses for stability. Always consult local building codes for walls over 3 feet.
- Excavate 6–12 inches deep for the base. Fill with 6 inches of compacted gravel. The first course should be buried at least 1 inch per foot of wall height.
- Batter is the backward lean (setback) of each course, typically 1 inch per foot of height. This improves stability by shifting the center of gravity toward the retained soil.
- Place 12 inches of clean crushed stone (3/4 inch) behind the wall for drainage. Add a 4-inch perforated drain pipe at the base. Wrap in filter fabric to prevent soil migration.