Retaining Wall Calculator

About the Retaining Wall Calculator

This retaining wall calculator estimates wall blocks, cap blocks, base gravel, drainage backfill, waste, and preliminary project cost. It is intended for early planning of segmental block walls and should be checked against the product system and local requirements.

Formula and assumptions

Blocks per row = round up wall length ÷ block length. Rows = round up wall height ÷ block height. Wall blocks = rows × blocks per row × (1 + waste). Caps = round up wall length ÷ cap length × (1 + waste). Gravel volume = length × width × depth, then apply waste and divide by supplier yield. Total cost adds blocks, caps, gravel, labor, and delivery.

Worked example

For a 20 ft wall at 3 ft high using 16 in × 6 in blocks, calculate 15 blocks per row and 6 rows: 90 wall blocks. With 10% waste, order 99 blocks. A 16 in cap gives 15 caps, or 17 with waste. A 10 ft³ base and 20 ft³ drainage zone become 11 and 22 ft³ after waste. At the sample prices, the estimated project total is about $1,191.

Measurement checklist

• Measure the wall face and account for corners or stepped sections.
• Use actual product dimensions and manufacturer system details.
• Confirm base thickness, drainage stone, perforated pipe, and backfill needs.
• Check slope, soil, surcharge, setbacks, and local permit requirements.
• Plan safe delivery and handling for heavy blocks and gravel.

Manual calculation steps

1. Convert block dimensions from inches to feet.
2. Divide length by block length and height by block height.
3. Round rows and blocks per row upward.
4. Estimate caps and gravel volumes.
5. Apply waste before rounding purchase quantities.
6. Add material, delivery, labor, and any engineering or permit costs.

Common mistakes

• Using nominal dimensions instead of actual block size.
• Ignoring the base and drainage zone.
• Skipping filter fabric or drainage pipe requirements.
• Relying on a calculator alone for tall or loaded walls.

Frequently asked questions