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Planning for a Block Retaining Wall

A retaining wall can prevent erosion and create a beautiful, terraced landscape. Use the instructions below to estimate materials for a retaining wall.

Retaining Wall in Landscape.

Calculating Material for Your Retaining Wall Project

Use the examples below as guides and adjust them to fit your project. Your material needs may vary depending on your specific design. Before you buy materials or begin work, check local building codes and your homeowner's association regulations to see if there are any restrictions or requirements you need to follow. A permit may be mandatory in some areas.

Good to Know

This guide provides instructions for estimating materials for a wall constructed of retaining wall blocks. For instructions on building a wall with concrete blocks (sometimes called cinder blocks) and mortar, see Laying Block.

Step 1

Estimate the number blocks you need for each course.

(length of the wall in inches) ÷ (length of a block) = blocks per course

Example: 228 in ÷ 11.5 in = approximately 20 blocks per course

Good to Know

Retaining wall blocks come in various sizes, so make your calculations accordingly.

Step 2

Determine the number of courses.

(height of the wall in inches) ÷ (height of a block) = number of courses

For example: 28 in ÷ 4 in = 7 courses

Good to Know

Remember the first course will be partially buried.

Step 3

Estimate the total number of blocks needed by multiplying the number of blocks per course by the number of courses.

(number of blocks per course) x (number of courses) = total number of blocks

20 blocks x 7 courses = 140 blocks

Good to Know

Purchase 10% more blocks than your estimate. The excess should account for breakage, cutting blocks and replacements for future repairs.

Step 4

Estimate the amount of paver base necessary. The paver base should be at least 2 inches deep when compacted. The calculation below factors in compaction.

(length of the wall in inches) x (depth of a block in inches x 2) x [(required depth of the base material in inches) + (required depth of the base material in inches x 0.20)] ÷ 1728 = cubic feet of base material

228 in x (7.5 in x 2) x [2 in + (2 in x 0.20)] ÷ 1728 = 4.75 cu ft of paver base

Good to Know

The recommended depth of paver base may vary by product.

Step 5

Estimate the amount of drainage aggregate that you need behind the wall.

(Length of the wall in inches) x (depth of a block in inches) x (height of the wall in inches) ÷ 1728 = cubic feet of drainage aggregate needed

228 in x 7.5 in x 28 in ÷ 1728 = approximately 28 cu ft of drainage aggregate