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Retaining Wall Calculator

A retaining wall holds back soil and prevents erosion. This calculator estimates the number of retaining wall blocks, base gravel, and cap stones for your project.

Enter Your Measurements

Results

Enter your measurements to see results

How to Use This Calculator

  1. Enter the total wall length in feet.
  2. Enter the desired finished height in feet.
  3. Enter the block face dimensions (check the product).
  4. Review block count, caps, and base gravel needed.

How Retaining Wall Calculation Works

This calculator divides wall area into block face area to determine total blocks needed, adds 5% for cuts and waste, and calculates cap stones for the top row. The base gravel estimate assumes a 6-inch deep, 24-inch wide compacted gravel trench — essential for proper drainage and stability. Walls over 4 feet typically require engineering, geogrid reinforcement, and possibly a permit.

Formula

Rows = Wall Height (in) ÷ Block Height. Blocks per row = Wall Length (in) ÷ Block Length. Total blocks = Rows × Blocks per row × 1.05. Cap stones = Blocks per row. Base gravel: 6 inches deep × 2 feet wide × Wall Length.

Frequently Asked Questions

How high can I build a retaining wall without a permit?
Most jurisdictions allow retaining walls up to 4 feet without a permit or engineering. Walls over 4 feet typically require a building permit and may need an engineer's design. Check local codes.
Do I need drainage behind a retaining wall?
Yes, always. Backfill with 12 inches of gravel behind the wall and install a perforated drain pipe at the base. Without drainage, water pressure builds up behind the wall and causes failure.
What base do I need for a retaining wall?
Dig a trench 6–8 inches deep and 24 inches wide. Fill with compacted gravel (crusher run works well). The first course of blocks should be partially buried below grade for stability.

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