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Retaining Wall Blocks Calculator
Estimate how many blocks you need to build a retaining wall of a given length and height.
Wall length
Wall height
Block length
Block height
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How it works
Blocks = (length ÷ block length) × (height ÷ block height), + ~5% waste
Blocks per row is the wall length divided by block length; courses is the height divided by block height. Multiply and add a small waste allowance for cuts and breakage.
Worked example
A 20 ft × 3 ft wall with 12"×4" blocks needs about 20 per row × 9 courses ≈ 189 blocks.
Frequently asked questions
Do I need a base course below grade?
Yes — bury the first course for stability. Include it in the height, plus a compacted gravel base.
When do I need engineering?
Walls over about 3–4 ft, or holding heavy loads, often need proper drainage, geogrid or an engineer’s design.
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This calculator is for educational purposes. Double-check important results before acting on them.