Retaining Wall Block Calculator: Blocks, Caps, Base and Drainage Stone
Enter wall length, height and block size. Get blocks, caps, base gravel, drainage stone and drain pipe in one buy list, with a course-by-course profile drawing. Feet or metres. Runs in your browser.
When to use this
- You are planning a low garden retaining wall from interlocking concrete blocks and want a first material list.
- You want blocks, caps, base gravel and drainage stone worked out together instead of blocks only.
- You want to see the courses and the setback drawn before you order.
How to use
- Choose feet or metres. Enter the wall length and the height above ground including the cap.
- Enter the block length, height and depth from the block maker, the cap size and the buried courses.
- Enter the setback per course, the gravel base and the width of drainage stone behind the wall.
- Press Calculate wall. Read the warnings, check the profile drawing and copy the buy list.
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Report a problem or suggest an improvement
Nothing is sent until you press Send. Your measurements are included only if you tick the box, and you can see the full report below first.
Examples
- 20 ft long, 3 ft high wall, 16 x 6 x 12 in blocks, 2 in caps: 6 courses above ground and 1 buried is 7 courses of 15 blocks: 105 blocks, 111 with 5 percent waste. Caps are 15, or 16 with waste. The base is 0.74 yd³ and the drainage stone 2.59 yd³ before the 10 percent spare.
- Taller wall: Raise the height above 4 ft and the tool shows a warning that such walls commonly need an engineer and a permit.
Understanding the result
The courses above ground are the wall height without the cap divided by the block height, rounded up, plus the buried courses. Blocks are the courses times the blocks in one course, plus waste. Caps cover the wall length. The base is the wall length times the base width times its thickness. The drainage stone is the wall length times its width times the height of the blocks. Both stone volumes get the spare percentage.
Limitations
- This estimates materials only. It is not a structural, drainage or permit check, and it does not say whether your wall is safe or allowed.
- Walls taller than about 4 ft (1.2 m), walls that carry a slope, driveway or building, and walls in poor soil commonly need an engineer and geogrid reinforcement. Check your local rules first.
- The stone density, the stone spare and the height warning are marked UNSOURCED. Always follow the instructions of your block maker.
- Curves, corners, steps, tiered walls and wall ends are not modelled. Run the tool once for each straight run or tier and add the lists.
- Geotextile fabric, geogrid, adhesive and backfill soil are not counted.
FAQ
How many retaining wall blocks do I need?
Divide the wall length by the block length and round up to get the blocks in one course, then multiply by the number of courses including any buried ones. Add waste. The tool does this and draws the courses.
How many courses should be buried?
Block makers usually give a rule, often one buried course for a low wall or about one tenth of the height for taller ones. The tool takes the number you enter, so follow your block maker.
How much gravel do I need behind the wall?
Many guides suggest a strip of clean crushed stone about 12 inches wide behind the wall for drainage, with a perforated pipe at the bottom. The tool counts the stone as the wall length times that width times the block height.
How tall can a DIY retaining wall be?
Rules differ, but many places ask for an engineer or a permit above about 4 feet. The tool warns when your wall is taller than that and does not judge whether a wall is safe.
What is setback?
Setback is how far each course steps back toward the hill. It leans the wall into the slope and helps it resist the soil. It is on the block maker's sheet.
Does this tool store my measurements?
No. It runs in your browser. The share link keeps your numbers after the # sign, which is never sent to a server.
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