Retaining Wall Calculator — Blocks, Backfill & Footing Estimate

Retaining Wall Design Basics

A retaining wall must resist the lateral pressure of the soil it holds back. Proper construction requires:

• Footing: Concrete base below frost line, typically 1 ft deep × 1.5× wall height wide, buried 1 inch for each foot of wall height
• Gravel base: 4–6 inch compacted gravel layer under the first course for drainage
• Gravel backfill: Crushed stone drainage layer (12 in wide) directly behind the wall face
• Drainage pipe: 4-inch perforated pipe at the base of the wall to relieve hydrostatic pressure
• Batter: Walls should lean back 1 inch per foot of height for dry-stack construction

Retaining Wall Material Comparison

• Segmental concrete block: Most common for DIY, interlocking, no mortar needed for walls under 4 ft, durable and consistent
• Natural stone (dry-stack): Attractive, requires more skill, irregular sizing makes estimation harder
• Landscape timber: Easy to work with, least expensive, but timber eventually rots (10–20 year lifespan)
• Poured concrete: Strongest option, requires formwork, rebar and professional work for walls over 4 ft

When You Need an Engineer or Permit

Most jurisdictions require permits and engineering review for retaining walls in these situations:

• Walls taller than 4 feet (3 feet in some areas)
• Walls supporting a structure, driveway or surcharge load above them
• Walls on slopes greater than 2:1 (horizontal:vertical)
• Walls near property lines or public roads
• Walls in areas with expansive or unstable soils

Always check with your local building department before starting construction.

Frequently Asked Questions