6x6 Timber Retaining Wall Calculator

Overview

Uses wall length and height to estimate stacked 6×6 timbers, gravel, drainage pipe, spikes, and backfill.

Assumptions

• A nominal 6×6 is treated as 5.5 in thick for the course count.
• The wall is a straight, level run.

Worked example

A 24-ft wall at 3 ft has ceil(36 ÷ 5.5) = 7 courses; with 8-ft timbers that is 3 per course × 7 = 21 face timbers, or 24 timbers after the tool adds 10% for cuts.

Common mistakes

• Forgetting buried course height.
• Choosing timber length without planning staggered joints.

Limitations

The tool does not calculate deadmen, tiebacks, footing, or soil pressure.

Safety and local requirements

Wear PPE when cutting treated wood and check local permit and drainage requirements before retaining soil.

Sources

• International Code Council — code reference background
• OSHA — Landscaping and Horticulture