Blocks (16"×8"): The total number of standard retaining-wall blocks needed for the face of the wall. This assumes a standard block with a 16-inch width and 8-inch height exposed face.
Wall Area: The total square footage of the wall face (length × height). This drives the block count calculation.
Cap Blocks: The number of cap or capstone blocks for the top course, estimated at one per linear foot of wall length.
Adhesive Tubes: Construction adhesive needed to secure the cap course, estimated at roughly two tubes per five linear feet of wall.
How This Calculator Works
You enter the wall's length and height in feet. The tool calculates total wall area, divides by the face area of a standard 16″×8″ block, and rounds up. Cap blocks are estimated at one per linear foot, and adhesive at two tubes per five feet. It assumes a straight wall with no corners, curves, or step-downs — add 5–10% extra for cuts and waste.
Quick Questions
How much waste should I add?
Plan for 5–10% extra blocks to cover cuts, breakage, and corners. Curved or stepped walls will need more waste allowance than straight runs.
Do I need a permit for a retaining wall?
Many jurisdictions require a building permit for walls over 4 feet tall (measured from the bottom of the footing to the top of the wall). Check your local building codes before starting.
What about the gravel base and backfill?
Most retaining walls need a compacted gravel base (typically 6 inches deep) and drainage gravel behind the wall. This calculator covers blocks and caps only — use a gravel calculator for base material.
Can I use different block sizes?
This tool assumes the common 16″×8″ face-area block. If your blocks are a different size, divide the wall area by your block's face area in square feet to get the count.