ft
Total length of the retaining wall
Enter wall lengthft
Exposed height above grade
Enter wall heightGravel backfill prevents hydrostatic pressure
Estimated Total Cost
—
📐 Important: Walls over 4 feet typically require permits and engineered plans. Always check local building codes. Add 10% waste to your block order. Bury the first course at least 1″ per foot of wall height (minimum 6″ below grade).
Was this calculator helpful?
How to Calculate Retaining Wall Materials
A retaining wall holds back soil on a sloped or elevated area. Calculating materials accurately saves money and prevents mid-project supply runs.
Block Count Formula
Blocks = (Wall Length ÷ Block Length) × (Wall Height ÷ Block Height)
For standard 12″×4″ (face) blocks on a 30 ft × 3 ft wall:
Length: 30 ft × 12 = 360 inches ÷ 12″ = 30 blocks per row
Height: 3 ft × 12 = 36 inches ÷ 4″ = 9 rows
Total: 30 × 9 = 270 blocks (+ 10% waste = 297 blocks)
Length: 30 ft × 12 = 360 inches ÷ 12″ = 30 blocks per row
Height: 3 ft × 12 = 36 inches ÷ 4″ = 9 rows
Total: 30 × 9 = 270 blocks (+ 10% waste = 297 blocks)
Drainage Gravel
Behind every retaining wall you need a layer of drainage gravel (typically ¾″ crushed stone) to prevent hydrostatic pressure buildup. Plan for 12 inches of gravel behind the wall, from the footing to 6 inches below the top.
💡 Pro tip: Install a perforated drain pipe at the base of your gravel layer — this is the most important step most DIYers skip. Without drainage, hydrostatic pressure builds up after rain and will eventually push your wall over, even a well-built one.
Popular Calculators
Related Calculators
Frequently Asked Questions
How many blocks do I need for a retaining wall?
Divide the wall length in inches by the block length, then divide wall height in inches by block height to get rows. Multiply to get total blocks and add 10% for waste. For standard 12″×4″ block, a 30-foot, 3-foot high wall needs approximately 270–300 blocks.
How much does a retaining wall cost?
Concrete block retaining walls cost $15–$30 per square foot for DIY materials, or $20–$60 per square foot professionally installed. Natural stone ranges from $25–$75 per square foot installed. A typical 50-foot, 3-foot wall (150 sq ft) costs $3,000–$9,000 installed.
Do I need a permit for a retaining wall?
Most jurisdictions require permits for walls over 4 feet high measured from the bottom of the footing. Some require permits starting at 3 feet. Always check local building codes before starting, especially for walls near property lines or over 4 feet tall.
How deep should a retaining wall footing be?
Bury the base course at least 1 inch per foot of wall height, with a minimum of 6 inches below grade. In frost zones, footings must extend below the frost line to prevent heaving. For a 4-foot wall, the base should be at least 4 inches underground.
What type of retaining wall lasts the longest?
Properly installed poured concrete and CMU walls last 50–100+ years. Natural stone dry-stack walls can last centuries with proper drainage. Timber walls typically last 20–40 years before deteriorating. Modular block walls typically last 20–50 years depending on drainage quality.