Retaining Wall Calculator
Enter the length and height of a segmental block wall to get the courses, blocks per course, cap blocks and the gravel it needs, with your own block price.
This retaining wall block calculator counts the blocks, cap blocks and gravel a segmental wall needs from its length and height. Pick a block face size or type your own, and it splits the wall into courses, tells you how many blocks each course takes, and adds a base leveling pad plus drainage stone behind the wall in cubic yards. As a quick wall material estimator it also totals the retaining wall cost from your price per block, so you can size the order before you visit the yard. Everything runs in your browser with nothing uploaded.
Wall
Blocks to buy
400
9 courses × 40 per course + 40 caps
- Courses
- 9
- Cap blocks
- 40
- Base gravel
- 1.48 yd³
- Material cost
- $2,000
Total gravel is about 5.93 yd³ — a 1.48 yd³ leveling pad under the first course plus 4.44 yd³ of drainage stone behind the wall. Plan on about 2 tubes of concrete adhesive to glue the caps down.
Counts assume a straight wall on a level base. Curves, corners, step-downs and buried courses change the block count, so add about 10% and check the block's actual laid dimensions with your supplier. Walls over 3–4 ft usually need engineering and geogrid.
How it works
- 1
Enter length and height
Add the wall run and the exposed height above grade. Switch between feet and metres any time.
- 2
Pick the block
Choose a 12×4, 16×6 or 18×8 in face, or type your own block width and height. Courses and blocks per course update as you go.
- 3
Add gravel and caps
Set the base pad depth and the drainage gravel behind the wall, toggle the cap row, and read the blocks, cubic yards and cost.
Instant & 100% private — nothing is uploaded
Every calculation runs locally in your browser. The income, balances and goals you enter stay on your own device and are never sent to a server — nothing is stored, logged or shared.
Frequently asked questions
- How many blocks does a retaining wall need?
- Split the height by the block face height to get the number of courses, then divide the length by the block width for the blocks in each course. Multiply the two. A 40 ft wall at 3 ft high with a 12×4 in block is 9 courses of 40 blocks, or 360 blocks before caps.
- Do I need cap blocks?
- Caps finish the top course and hide the hollow cores. Turn the cap row on and the tool adds one course of caps equal to the blocks in a single row, plus an estimate of the concrete adhesive tubes to glue them down. Leave it off if your block system is solid or you are capping a different way.
- How much gravel goes behind a retaining wall?
- Two lots: a compacted base pad under the first course, usually about 6 inches deep, and a column of free-draining stone behind the wall the full height. The estimator reports both in cubic yards from your wall length, height and the thickness you set, so drainage is not left out of the order.
- How is the retaining wall cost worked out?
- It multiplies the blocks and caps by your own price per block. Enter a local quote and the total tracks it live. The figure covers block only, so add gravel, adhesive, drain pipe, fabric and delivery from your supplier for a full budget.
- How tall can I build without an engineer?
- Most areas let a homeowner build a segmental wall up to about 3 to 4 ft. Above that, or on a slope or under a driveway, walls usually need a design with geogrid reinforcement and a permit. Check your local rules before you order.
- Does it handle curves and corners?
- The counts assume a straight run on a level base. Curves, corners, steps and courses buried below grade all change the block count, so treat the number as a close estimate and add roughly 10% for cuts and waste.
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