How many retaining wall blocks do I need?

Divide the total wall face area (Length × Height) by the face area of one block, then add 5% for cuts and waste. For a common Allan Block (0.667 ft² face), a 20×3 ft wall = 60 ft² ÷ 0.667 = 90 blocks × 1.05 ≈ 95 blocks.

Do retaining walls need a gravel base?

Yes. A compacted gravel base is essential for drainage and stability in retaining walls. Without proper drainage, hydrostatic water pressure builds behind the wall and can cause it to heave or fail. Typically 6 inches of compacted crushed stone is installed at the base of the foundation trench.

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🛠️ Construction & DIY

Retaining Wall Block Estimator

Estimate the number of retaining wall blocks and base gravel needed based on wall dimensions.

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Wall Length (ft)

Wall Height (ft)

Block Face Area (ft²)

Retaining Wall Block Estimator

Retaining Wall Blocks

Retaining Wall Block Estimation