Retaining Wall Block Calculator
This calculator turns each wall run's length and exposed height into a material take-off for a dry-stacked segmental retaining wall (SRW): the number of blocks by course, the cap course, the buried base course, the crushed-stone leveling pad and drainage stone, an optional geogrid suggestion, the setback and batter, and an itemised cost. It works course by course rather than by a flat area rule, so burial, batter and the cap are all counted rather than glossed over.
Enter as many wall runs as your project needs — stepped, tiered or L-shaped walls are just several runs — and the totals sum across all of them. Switch between metric and imperial at any point, export a CSV or print a take-off sheet. Everything is calculated in your browser: nothing is uploaded and no sign-up is needed.
This is a material estimator, not an engineering tool. It does not perform global stability, bearing, sliding, overturning, surcharge or seismic checks. Walls above roughly 1.2 m (4 ft), or any wall with a slope above it, a surcharge such as a driveway, or poor soil, should be designed by a licensed engineer. The geogrid and burial figures here are common industry rules of thumb, not an engineered reinforcement design.
How to use the calculator
Pick a block size, add your wall runs, and read the quantities live in the results rail as you type. The block count for a run is the number of courses (total height divided by block height, rounded up) multiplied by the blocks per course (run length divided by block face width, rounded up), plus a waste allowance. Because SRW blocks are dry-stacked, the blocks-per-course uses the face width directly — there is no mortar joint to add.
The cap course is counted separately from its own face width, and dry-stack construction adhesive replaces mortar: one tube covers about 7.6 m (25 ft) of cap by default. The base and drainage stone are estimated as crushed stone through the same take-off maths as the gravel calculator, so the tonnage, truck loads and bag counts are consistent with that tool.
How to estimate a retaining wall in 5 steps
- Choose unitsPick metric or imperial at the top of the page. Every input, result and diagram label converts as you switch.
- Pick a blockChoose a block size class — or Custom to enter your own length, height, depth and setback — and a matching cap. Sizes are dimension classes, not brand names.
- Add your wall runsEnter the length and exposed height of each straight run of wall. Add a run for each leg of a stepped, tiered or L-shaped wall; the totals sum across them.
- Set the base and drainageReview the leveling-pad width and depth, the drainage-stone width and the drain pipe and filter fabric. Defaults are prefilled from common practice and are fully editable.
- Read the resultsRead the block, cap and adhesive counts, the base and drainage tonnage, the geogrid suggestion, and the setback and batter. Add prices for a cost, then export a CSV or print the take-off.
The parts of a segmental retaining wall
A dry-stacked SRW is built from a few repeating parts. The blocks are stacked in courses on a compacted crushed-stone leveling pad, with the lowest course or two buried below finished grade to lock the wall against sliding. A cap course is adhered to the top with construction adhesive to finish the wall and shed water.
Behind the wall face sits a column of free-draining crushed stone with a perforated drain pipe at its base, so water pressure never builds up behind the blocks. The retained soil is held back by the wall and, on taller walls, by layers of geogrid that extend back into that soil. Each course steps back slightly from the one below, giving the wall its backward lean, or batter.
The buried base course
Burying the bottom of a wall is what stops it sliding forward under the push of the soil behind it. A common rule of thumb is to bury about 1 inch of wall for every 1 foot of exposed height, with a minimum of about 150 mm (6 in). This calculator applies that rule to the exposed height — buried depth = max(exposed height ÷ 12, 150 mm) — and adds enough whole courses to reach it, so the buried block is included in the count rather than forgotten.
You can turn burial off or type your own buried depth if your site or block supplier calls for something different. The buried depth, the number of buried courses and the resulting total height all update in the results and on the cross-section. This burial figure is an industry rule of thumb, not an engineered embedment — confirm it against your block manufacturer's instructions and local practice.
Setback and batter
Setback is how far each course steps back from the one below it; batter is the resulting backward lean of the wall face. A small backward lean helps a gravity wall resist the soil behind it. The setback is a property of the block — a common generic value is about 19 mm (¾ in) per course — so the calculator reads it from the chosen block and lets you edit it for a custom block.
The total setback is the per-course setback multiplied by the number of courses, and the batter angle is the arctangent of the setback over the block height. Both values are shown in the results and drive the lean you see on the live cross-section. A setback of zero simply gives a vertical wall.
Geogrid reinforcement
Geogrid is a stiff plastic mesh laid horizontally between courses of block and extending back into the retained soil, tying the soil mass and the wall together so they act as one. Taller walls generally need it; shorter ones usually do not. This calculator suggests geogrid only above roughly 1.2 m (4 ft) of total height, and lets you force it on or off.
When geogrid is on, the tool estimates a layer every couple of courses (capped so the vertical spacing stays within about 600 mm), an embedment length back into the slope, and the total reinforced area and roll length. These numbers are informational only. Real geogrid layout depends on the soil, the slope above the wall, any surcharge and the specific product, and varies widely from site to site — treat the figures as a rough planning aid and have a professional engineer design the reinforcement for any wall that needs it.
Worked examples
A 6 m long wall with 1.0 m of exposed height, built from a standard block about 450 mm wide and 200 mm high: the buried depth is max(1.0 ÷ 12, 0.15) = 0.15 m, so total height is about 1.15 m, which is 6 courses. Blocks per course is 6.0 ÷ 0.45 rounded up to 14, giving about 84 blocks before waste, plus a cap course of about 14 units and two tubes of adhesive. Because the wall is under 1.2 m, geogrid is only suggested if you force it on.
A taller 3 m long wall with 1.4 m exposed crosses the 1.2 m threshold: it triggers both the geogrid suggestion and the engineering-scope notice, because a wall this tall should be checked by an engineer. Add several runs — for a stepped or tiered wall — and the block, cap, adhesive, base and drainage-stone totals sum across every run, so you get one combined order. These figures are estimates; always confirm block dimensions and quantities with your supplier before ordering.
Frequently asked questions
How many blocks do I need for a retaining wall?
Work it out course by course. Divide the total height (exposed height plus the buried base) by the block height and round up to get the number of courses, then divide the wall length by the block face width and round up to get the blocks per course. Multiply the two and add a waste allowance. For a 6 m wall 1.0 m high in a 450 × 200 mm block that is about 6 courses × 14 = 84 blocks before waste. This calculator does the rounding and waste for you.
Do I need to bury the bottom course?
Yes, for almost every wall. Burying the base course below finished grade stops the wall sliding forward under the soil load. A common rule of thumb is to bury about 1 inch of wall per foot of exposed height, with a minimum of around 150 mm (6 in). The calculator applies this rule by default and adds the buried course to the block count; you can turn it off or enter your own depth.
How much base and drainage gravel do I need?
The leveling pad is a compacted crushed-stone layer under the wall — roughly the block depth plus 300 mm wide and about 150 mm deep — and the drainage stone is a column of free-draining crushed stone behind the wall, the full exposed height and about 300 mm wide. The calculator estimates both as crushed stone and reports the tonnage, loose volume, truck loads and bag counts, using the same take-off maths as the gravel calculator.
What are setback and batter?
Setback is how far each course steps back from the one below; batter is the backward lean of the finished wall face that results. The setback is a property of the block — about 19 mm (¾ in) per course is common — and the batter angle is the arctangent of the setback divided by the block height. A slight batter leans the wall into the hill and helps it resist the soil; a setback of zero gives a vertical wall.
Do I need geogrid reinforcement?
Usually only on taller walls. Geogrid is a mesh laid between courses and extending into the retained soil to tie the soil and wall together. As a rough guide, walls above about 1.2 m (4 ft), or any wall with a slope or surcharge above it, often need it, while shorter garden walls usually do not. This tool suggests geogrid above that height as an informational estimate only — the actual layout must be designed by a professional engineer.
How many cap units and adhesive tubes do I need?
Cap units are counted from the cap face width: divide the wall length by the cap width, round up and add a little waste. Because the wall is dry-stacked, caps are glued down with construction adhesive rather than mortared — one tube covers about 7.6 m (25 ft) of cap by default, which you can adjust. The calculator reports both the cap count and the number of adhesive tubes.
How many courses tall will my wall be?
Divide the total height — the exposed height plus the buried base depth — by the block height and round up. A 200 mm block over a 1.15 m total height is about 6 courses. The buried base adds courses below grade, so a wall that shows 1.0 m of face is usually a course or two taller than it looks. The calculator shows the course count for each run and the tallest run overall.
Does the calculator work in metric and imperial?
Both. Switch units at the top and every dimension converts — wall length and height, block and cap sizes, pad and drainage dimensions, setback and the diagram labels. The engine works in SI internally and only converts for display, so switching units never changes the underlying counts.
Is the retaining wall calculator private?
Yes. Every calculation runs entirely in your browser. Nothing you enter is sent to a server, and your wall runs and settings are saved only in your own browser's local storage so they are still there when you come back.