Retaining Wall Calculator

How It Works

Retaining walls hold back soil on sloped yards. This calculator figures out how many blocks you need based on wall dimensions and block size, then estimates the base gravel and drainage gravel required for a properly engineered wall.

The Formula

Variables

• WallLength_in — Wall length converted to inches
• WallHeight_in — Wall height converted to inches
• BlockLength — Face length of one block in inches
• BlockHeight — Face height of one block in inches
• 1.05 — 5% waste factor for cutting end blocks

Example

A 20 ft long, 3 ft high wall with 12" x 4" blocks: 20 blocks per row, 9 courses high = 180 blocks. With 5% waste = 189 blocks. At $3.50 each, block cost is $661.50.

Tips

• Walls over 4 feet tall typically require engineering plans and permits -- check your local codes.
• The first course should be buried 1 inch per 8 inches of wall height for stability.
• Always use compacted gravel (not dirt) as the base -- it does not settle or wash away.
• Install a perforated drain pipe behind the bottom course to prevent water pressure buildup.
• Stagger block joints between courses (like brickwork) for maximum structural strength.