🧱 Retaining Wall Calculator
Calculate blocks and materials needed for retaining walls
How to Use This Calculator
Enter Wall Dimensions
Input the length and height of your retaining wall in feet. Measure the total wall area where you'll be installing retaining wall blocks.
Select Block Type
Choose your retaining wall block type: Standard (12×8 inch blocks) or Large (18×8 inch blocks). Check your block product specifications for exact dimensions.
Specify Base Depth
Select the base material depth in inches. Standard is 6 inches for walls up to 4 feet tall. Taller walls may need 8-12 inches of base material for stability.
Calculate and Order
Click "Calculate Retaining Wall" to see blocks needed, base material (crushed stone), and drainage gravel (behind wall). Add extra for curves, corners, and mistakes.
Formula
Blocks per Row = Wall Length (inches) ÷ Block Length (inches)
Rows Needed = Wall Height (inches) ÷ Block Height (inches)
Total Blocks = Blocks per Row × Rows Needed
Blocks to Order = Total Blocks × 1.10 (includes 10% waste)
Base Material = Wall Length × Base Depth × (Base Depth ÷ 12) ÷ 27 (cubic yards)
Example 1: Standard Wall (20 ft × 4 ft, 12×8 inch blocks, 6 inch base)
Step 1: Convert dimensions: 20 ft = 240 inches, 4 ft = 48 inches
Step 2: Blocks per row: 240 ÷ 12 = 20 blocks
Step 3: Rows needed: 48 ÷ 8 = 6 rows
Step 4: Total blocks: 20 × 6 = 120 blocks
Step 5: Add waste: 120 × 1.10 = 132 blocks (with 10% waste)
Step 6: Base material: (20 × 0.5 × 0.5) ÷ 27 = 0.19 cubic yards
Example 2: Tall Wall (30 ft × 6 ft, 12×8 inch blocks, 8 inch base)
Step 1: Convert dimensions: 30 ft = 360 inches, 6 ft = 72 inches
Step 2: Blocks per row: 360 ÷ 12 = 30 blocks
Step 3: Rows needed: 72 ÷ 8 = 9 rows
Step 4: Total blocks: 30 × 9 = 270 blocks
Step 5: Add waste: 270 × 1.10 = 297 blocks (with 10% waste)
About Retaining Wall Calculator
The Retaining Wall Calculator is an essential tool for homeowners, landscapers, contractors, and DIY enthusiasts who need to accurately determine how many retaining wall blocks are required for their retaining wall projects. This calculator eliminates guesswork by providing precise block counts, base material quantities, and drainage gravel estimates, helping you order the right amount of materials without waste or shortages.
When to Use This Calculator
- Garden Retaining Walls: Calculate blocks needed for garden terraces, raised beds, or landscape features
- Property Line Walls: Determine materials for property boundary retaining walls
- Slope Management: Estimate materials for retaining walls to manage slopes and prevent erosion
- Driveway Retaining Walls: Calculate blocks needed for driveway edge retaining walls
- Budget Planning: Calculate material costs by determining exact block and material quantities needed
Why Use Our Calculator?
- ✅ Accurate Block Count: Precise calculations prevent over-ordering or running short
- ✅ Base Material: Calculates crushed stone needed for stable foundation
- ✅ Drainage Gravel: Estimates drainage gravel needed behind the wall for proper drainage
- ✅ Multiple Block Sizes: Supports standard (12×8) and large (18×8) block sizes
- ✅ Cost Planning: Helps budget accurately by determining exact material needs
- ✅ Time Savings: Instant calculations eliminate manual math and measurements
Common Applications
Garden and Landscape Walls: Homeowners and landscapers planning garden terraces or landscape features use this calculator to order the correct quantity of retaining wall blocks. Standard retaining walls use 12×8 inch blocks, which this calculator helps determine accurately.
Property Boundary Walls: Contractors and property owners planning property line retaining walls use this tool to estimate block quantities needed. Retaining walls require proper base material (crushed stone) and drainage gravel for stability.
Slope Management: Homeowners and contractors planning retaining walls to manage slopes use this calculator to determine block quantities needed, ensuring sufficient materials are on-site before starting work.
Tips for Best Results
- Base Material: Standard base depth is 6 inches; taller walls (6+ feet) need 8-12 inches
- Drainage: Always include drainage gravel behind the wall (6 inches deep) for proper drainage
- Add Waste: Always add 10% extra for waste, cuts around curves/corners, and mistakes
- Geogrid: Tall walls (4+ feet) may require geogrid reinforcement—consult engineering specifications
- Local Codes: Check local building codes for retaining wall height limits and permit requirements
Frequently Asked Questions
How many blocks do I need for a 20×4 foot retaining wall?
A 20×4 foot retaining wall using standard 12×8 inch blocks requires approximately 132 blocks (including 10% waste). Without waste, you'd need 120 blocks (20 blocks per row × 6 rows). Always add 10% extra for cuts and mistakes.
How deep should the base be for a retaining wall?
Standard base depth is 6 inches for walls up to 4 feet tall. Taller walls (4-6 feet) need 8 inches, and very tall walls (6+ feet) need 10-12 inches. The base should extend 6 inches beyond the wall width on both sides.
Do I need drainage gravel behind the wall?
Yes! Always include drainage gravel (crushed stone) behind the wall (6 inches deep) for proper drainage. Without drainage, water pressure can damage or collapse the wall. Use perforated drain pipe at the base for tall walls.
How much does a retaining wall block cost?
Retaining wall block prices vary by type and brand: standard blocks $2-$5 each, decorative blocks $3-$8 each, premium blocks $5-$15 each. Prices depend on material, size, and brand. Budget blocks are cheaper; premium materials cost more.
Do I need a permit for a retaining wall?
Many areas require permits for retaining walls over 3-4 feet tall. Check local building codes for height limits and permit requirements. Taller walls may require engineering approval. Always check before starting construction.
Can I build a retaining wall myself?
Short walls (under 3 feet) are often DIY-friendly with proper base preparation and drainage. Taller walls (4+ feet) may require professional installation and engineering. Always follow manufacturer instructions and local building codes.