Retaining Wall Block Calculator
Enter wall length and height to get block count using standard 12×4×8" retaining wall blocks, cubic yards of compacted gravel base, drain pipe length, and total material cost.
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Top PickRetaining Wall Blocks — Home Depotfrom $4.48/block* Affiliate links — we may earn a commission at no cost to you.
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
How many retaining wall blocks do I need for a 20-ft wall, 3 ft tall?
Using standard 12×4-inch blocks: 3 ft exposed + 1 buried course = 10 courses high. Each course needs 20 blocks for 20 linear feet. That's 200 blocks plus 5% waste = 210 blocks.
Does a retaining wall need drainage?
Yes — hydrostatic pressure from water-saturated soil is the primary cause of retaining wall failure. Always install a 4" perforated drain pipe behind the base course and backfill with clean crushed stone, not soil. Weep holes every 4–6 feet also help.