Retaining Wall Calculator
You need your wall area divided by the face area of one block, plus 5% for breakage, a cap row on top, and a gravel base below. Enter the sizes to get blocks, caps, base, and cost.
How to estimate retaining-wall blocks
Find the wall face area (length × height) and divide by the face area of one block. Add 5% for the pieces that crack or get cut at the ends. A taller wall may need to step back or include geogrid — check local codes above about 3 to 4 feet.
Caps and base
Finish the top with a single row of cap blocks along the full length. Below the first course, dig a leveling trench and fill it with a compacted gravel base about 6 inches deep — the calculator returns that volume so you can order aggregate.
Drainage matters
Backfill behind the wall with free-draining gravel; size it with the cubic yard calculator. For a flat patio instead of a wall, use the paver calculator.
Frequently asked
How many blocks do I need for a retaining wall?
Divide the wall face area by the face area of one block, then add 5% for breakage. A 20 ft × 3 ft wall with 12×8 in blocks needs about 95 blocks plus a cap row.
Do I need cap blocks?
Cap blocks finish the top course and protect the wall. You need one row along the full length — about one cap per block length across the top.
How much gravel base does a retaining wall need?
Lay a compacted gravel base roughly 6 inches deep and a foot wide in a leveling trench. The calculator returns that base volume in cubic yards.