Retaining Wall Calculator: Block, Stone and Timber Options

A retaining wall holds back soil and creates level ground where the terrain would otherwise slope. Getting the design and materials right is important — a poorly built retaining wall can collapse, causing property damage or injury. This guide covers material options, quantity calculations, and cost estimates for the three most popular DIY retaining wall types.

When Do You Need a Retaining Wall?

Retaining walls are needed when you’re creating a level terrace on a slope, preventing soil erosion near driveways or walkways, managing drainage, or creating raised garden beds. Any wall over 4 feet tall (measured from the base of the footing) typically requires a building permit and may need engineering. Walls under 4 feet can often be built as a DIY project.

Concrete Block Retaining Walls

Segmental retaining wall blocks (like Allan Block or Versa-Lok) are the most popular DIY option. Standard blocks are 12 inches deep, 8 inches tall, and 18 inches long. The number of blocks needed = (wall length in feet × 0.75 blocks per linear foot) × number of courses. Each course is approximately 6-8 inches of height. For a 30-foot wall, 3 feet tall: approximately 30 × 0.75 × 5 = 112 blocks. Add 5-10% for cuts and waste. Block prices range from $3-$6 each; installed cost runs $15-$30 per square foot of wall face.

Natural Stone Retaining Walls

Dry-stacked fieldstone and cut stone walls are beautiful but require experience to build properly. Natural stone weighs 150-170 pounds per cubic foot. For a rough estimate, a 1-foot thick wall contains about 1 cubic foot of stone per square foot of face. Natural stone costs $200-$400 per ton, with each ton covering approximately 30-40 square feet of wall face. Professional installation adds $30-$50 per square foot.

Timber Retaining Walls

6×6 or 8×8 pressure-treated landscape timbers are an economical choice for walls under 4 feet. Timber walls require deadman anchors (horizontal timbers running perpendicular into the hillside) every 4-6 feet for stability. Landscape timber costs $15-$30 per 8-foot length. Timber walls have a shorter lifespan (15-25 years) than block or stone walls.

Drainage Is Critical

All retaining walls need drainage. Hydrostatic pressure (water pressure buildup) is the leading cause of retaining wall failure. Install a gravel drainage layer behind the wall and perforated drain pipe at the base. Without proper drainage, any wall will eventually fail.

Estimate your wall materials. Use the Retaining Wall Calculator on diycalculator.net to calculate blocks, stone, or timber needed for walls of any dimension.