How many retaining wall blocks do I need?

Divide the wall face area by the face area of one block, then add waste. A standard 12 × 8 in block covers about 1.5 blocks per square foot of wall.

Do retaining wall blocks need mortar?

Most segmental retaining-wall blocks are dry-stacked and interlock or pin together — no mortar. This calculator assumes a dry-stack (zero joint).

How deep should the base of a retaining wall be?

Plan a buried base course (often the first course below grade) on 4–6 inches of compacted gravel. Use the gravel calculator for the base material.

Retaining Wall Calculator

Work out how many blocks you need for a segmental retaining wall. Enter the wall size and your block's face dimensions to get the block count plus an estimate of courses and blocks per course.

Retaining wall calculator

Segmental retaining-wall blocks are dry-stacked (no mortar). The count is for the wall face; add a base course below grade and a separate cap row if your block system uses caps.

How it's calculated

We take the wall face area (length × height), work out the face area of one dry-stacked block — (length × height) ÷ 144 for square feet — divide one by the other, add a waste allowance, and round up. Courses and blocks per course come from the wall and block dimensions.

Frequently asked questions

How many retaining wall blocks do I need?: Divide the wall face area by the face area of one block, then add waste. A standard 12 × 8 in block covers about 1.5 blocks per square foot of wall.
Do retaining wall blocks need mortar?: Most segmental retaining-wall blocks are dry-stacked and interlock or pin together — no mortar. This calculator assumes a dry-stack (zero joint).
How deep should the base of a retaining wall be?: Plan a buried base course (often the first course below grade) on 4–6 inches of compacted gravel. Use the gravel calculator for the base material.

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Last updated June 2026.