Retaining Wall Calculator
Retaining walls are counted in courses: rows of blocks stacked to the wall height. Enter your wall and block face size to get courses, blocks per course, caps, and the order quantity. Runs 100% in your browser.
Retaining Wall Calculator
About this retaining wall calculator
Retaining wall blocks are counted in two steps, not by area: first the courses (rows) from wall height divided by block face height, then the blocks per course from wall length divided by block face length. Multiply the two and you have the wall. Area math alone undercounts, because a half-block remainder at the end of every course still costs a full block. Our retaining wall guide covers buried courses, caps, drainage, and the 4-foot engineering line.
Use the block's actual face dimensions, not its nominal size: a block sold as 16 inches long is often 15-5/8 inches on the face once the joint is counted, and that 3/8-inch difference adds up over a long wall. If your product's spec sheet gives a different face size, the math here still works — it divides your wall by whatever face size you enter, so enter the real one.
The buried base course is the step most first-timers skip. The first course sits below finished grade — at least one full block height, or 10% of total wall height — so the wall height you enter here should be the total height including that buried course, not just the height you see above ground. Caps are counted separately: one cap per block on the top course, glued in place, and usually priced separately from wall blocks.
How to use
- Measure your wall length in feet along the face of the wall.
- Enter the total wall height in feet, including the buried base course.
- Choose your block's face length and height from the product spec (16 × 8 in is standard).
- Pick a waste allowance — 10% for straight walls, 15% for corners and curves — and optionally a price per block.
- Press Calculate for courses, blocks, caps, and the order quantity.
Good to know
- Straight walls only — stepped, curved, and terraced walls need layout per section; curves waste more block.
- This counts segmental dry-stacked blocks only. Mortared CMU retaining walls, poured concrete, and timber walls use different materials and need separate estimates.
- Does not size geogrid, footings, or drainage gravel — and it does not say a wall is safe. Most jurisdictions require engineering above 3–4 feet of exposed height, and surcharge loads (driveway, slope, or building above the wall) lower that threshold.
Frequently asked questions
How many retaining wall blocks do I need for a 20-foot wall?
It depends on height: a 20 ft long, 2 ft high wall with 16 × 8 in blocks is 3 courses of 15 blocks = 45 blocks — order 50 with 10% waste, plus 15 cap blocks.
How many blocks per square foot of retaining wall?
Roughly 1 block per 0.89 sq ft for a 16 × 8 in face, but course rounding at the ends of the wall is why this calculator counts whole blocks per row instead of dividing area.
How deep should the base course be buried?
At least one full block height, or 10% of the total wall height, whichever is more. For a typical 8-inch unit that is at least 8 inches below finished grade.
How many cap blocks do I need?
One cap per block on the top course — the same as blocks per course. Caps are flat finishing units, usually glued, and usually priced separately.
How tall can a retaining wall be without an engineer?
Most jurisdictions set the trigger at 3–4 feet of exposed height, and surcharge loads above the wall can lower it. Check with your building department before you dig.