The intentional backward lean of a retaining wall, typically 1 inch per foot of height. This lean uses gravity to counteract soil pressure.
Geogrid
A synthetic mesh fabric embedded in the backfill soil behind the wall to increase its effective weight and resistance to soil pressure.
Drainage Aggregate
Clean, crushed gravel placed behind the wall to allow water to flow freely to the drain pipe, preventing hydrostatic pressure buildup.
Surcharge
Any additional load placed on top of the retained soil, such as a driveway, parked vehicles, or a structure, which increases the lateral pressure on the wall.
Deadman Anchor
A perpendicular timber or concrete element extending back into the hillside to anchor the wall against sliding or overturning forces.
Result: 27 blocks/row × 8 rows = 216 blocks × 1.10 = 238 blocks. Geogrid required every 2 courses. Need engineering review for walls over 4 feet.
Retaining Wall Materials
Material
Max DIY Height
Cost per Sq Ft
Durability
Interlocking Block
3–4 ft
$12–$22
50+ years
Natural Stone
2–3 ft
$15–$30
Lifetime
Timber (6×6)
3 ft
$10–$18
10–15 years
Poured Concrete
Engineered
$20–$45
50+ years
Boulder
2–3 ft
$20–$40
Lifetime
Retaining Wall Design Essentials
Drainage Is the Top Priority
Water pressure behind a retaining wall is the leading cause of failure. Every wall needs a perforated drain pipe at the base, wrapped in filter fabric, surrounded by clean gravel, and daylighting to a lower elevation. Without proper drainage, hydrostatic pressure can double or triple the force the wall must resist.
When You Need an Engineer
Most building codes require engineered plans for retaining walls over 4 feet tall (measured from the bottom of the footing to the top of the wall). Walls near property lines, structures, slopes, or carrying surcharge loads may also require engineering regardless of height. The cost of an engineer is minor compared to rebuilding a failed wall.
Frequently Asked Questions
How do I calculate how many retaining wall blocks I need?
Calculate the total face area of the wall (Length × Height) and divide by the face area of a single block. Our calculator handles this automatically and adds a configurable safety margin.
Why should I bury the first row of blocks?
Burying the bottom row ("keying" the wall) is essential for structural stability. It prevents the base of the wall from sliding forward under the weight of the soil behind it. This is one of the most common DIY mistakes.
What is the purpose of gravel backfill?
Gravel backfill prevents hydrostatic pressure (water pressure) from building up behind your wall. Without proper drainage, water-saturated soil can become heavy enough to push over even the strongest walls.
When do I need to use geogrid reinforcement?
Most retaining walls over 3–4 feet in height require geogrid. This high-strength mesh ties the block face into the consolidated soil behind the drainage zone, preventing tipping and overturning failure.
Do I need a building permit for my retaining wall?
Permit requirements vary by jurisdiction, but most areas require permits for walls over 4 feet tall (measured from the bottom of the footing). Walls near property lines or under surcharge loads may require permits regardless of height. Always check with your local building department.
What is the difference between running bond and stack bond?
Running bond staggers the vertical joints between courses, similar to how bricks are laid. This creates a stronger wall by distributing lateral forces. Stack bond aligns vertical joints and is weaker structurally but can be used for low decorative walls.
How do I account for a sloped yard behind my wall?
Enable the "Sloped Backfill (3:1)" toggle in the calculator. This increases the effective soil pressure on the wall, requiring wider drainage gravel and potentially triggering geogrid requirements at a lower wall height.
Can I build a retaining wall as a DIY project?
DIY projects are generally safe for walls under 3 feet. For taller walls, always check local building codes — permit requirements and structural engineering reviews often apply. Segmental block walls are the most DIY-friendly option for heights up to 4 feet.
Related Calculators
How to Use This Calculator
1
Measure Wall Length and Height
Enter the total wall run length and the exposed height in feet. For tiered walls, calculate each tier separately.
2
Choose Block Type
Select your retaining wall block size and style. Common dimensions are 12x4x8 inches and 18x6x12 inches.
3
Enter Setback and Batter
Specify the setback (backward tilt per course). Most segmental retaining wall systems use a 3/4-inch to 1-inch setback per course.
4
Calculate Base Width
The base width should be at least 0.6x wall height for walls under 4 feet. Taller walls require engineering review.
5
Get Block Count and Base Gravel
Review total blocks, compacted gravel for the base and backfill, drainage pipe length, and geogrid requirements for taller walls.
Key Formulas
Base WidthBase = 0.6 x Wall Height
Blocks per CourseBlocks/Course = Length / Block Length
Total CoursesCourses = Height / Block Height
Drainage GravelBackfill: 12 in gravel layer behind wall
Key Terms
Setback / Batter — The intentional backward tilt of the wall per course, typically 3/4 to 1 inch per course. This lean uses gravity to help resist soil pressure behind the wall.
Deadman / Anchor — A block or block combination extended perpendicular into the hillside to tie the wall into the retained soil for walls over 3 feet tall.
Geogrid — A polymer mesh embedded horizontally in the backfill at prescribed intervals to create a mechanically stabilized earth mass behind tall walls.
Drainage Aggregate — Clean crushed stone (3/4-inch) placed in the 12-inch zone immediately behind the wall to carry groundwater to the weep holes and drainage pipe.
Frost Heave — The upward displacement of soil and structures caused by freezing groundwater expanding in the soil. Proper drainage prevents ice accumulation that causes frost heave.
Surcharge Load — Additional load on the retained soil from structures, vehicles, or slopes above the wall that increases lateral pressure and must be accounted for in wall design.