Retaining wall calculator

Measure the wall, then count the courses

Measure the length along the actual wall alignment. For a straight wall, that is the end-to-end length. For a curve, use the arc length along the line where you measured your block width. Do not substitute the straight chord across the curve. Divide a wall with changing heights into sections and estimate each section separately.

Enter the exposed height of the block face, excluding the cap, and the number of buried courses shown on your plans. The calculator rounds the exposed height up to a full course, then adds the buried courses. A desired height of 37 inches with 6-inch-high units therefore needs seven exposed courses, not 6.17 courses. That means 42 inches of constructed exposed blockwork before the cap.

For each section, it also rounds the number of units across one course up to a whole unit. It multiplies the two rounded counts before adding a cutting and breakage allowance. This is a purchasing estimate: a cut piece may be reused, corner units may be different, and a manufacturer’s pattern can change the final schedule.

Units per course = ceil(length ÷ unit length)
Courses = ceil(exposed height ÷ unit height) + buried courses
Order units = ceil(units per course × courses × (1 + waste ÷ 100))

Keep leveling base and drainage stone separate

The leveling pad and the drainage zone are different quantities. The first is a long rectangular prism beneath the wall. The second is the stone-filled space behind it. You may need different aggregate products for the two tasks, and they may have different prices. This tool reports them separately so you can request the correct quantities from a supplier.

Base volume equals wall length times the entered trench width times the entered compacted base depth. Trench width is the block depth plus your extra width allowance. Drainage volume uses the entered width behind the wall and the constructed wall height less your top soil-cap depth. A soil cap deeper than the wall produces zero drainage height rather than a negative result.

The default dimensions are illustrative planning inputs. Allan Block’s residential installation guide is one example that specifies a 6-inch base and a 12-inch stone zone behind its blocks. These details are product-specific; confirm the details for the wall system and site you will actually build.

Base volume = length × trench width × compacted base depth
Drainage volume = length × drainage width × drainage height
Cubic yards = cubic feet ÷ 27

Include buried units, caps, and hollow cores

Buried units still have to be ordered even though they are not visible in the finished wall. They are included in the wall-unit total, and the takeoff shows their count separately. The one-course starting setting is editable. It is not a universal embedment specification, frost-depth determination, or assurance that a particular foundation is adequate.

Caps often have a different length from face units. Enter the actual cap coverage measured along the wall; the calculator rounds up cap counts for each section and then adds the cutting allowance. Tapered caps on curves may need cuts and may cover a different run than the catalog’s maximum width.

Some hollow blocks need stone in their cores. Enter the supplier’s fill volume per unit if applicable. The starting value is zero because solid units and hollow products have different fill requirements. Core fill is added to the drainage-stone quantity; structural concrete grout is a separate product and is outside this segmental-wall estimator.

Convert volume to order weight carefully

Cubic yards and cubic metres describe volume. Tons and tonnes describe mass. A quarry’s conversion depends on the material, moisture, grading, and whether the quoted density is loose or compacted. The estimator starts at an illustrative 1.4 US short tons per cubic yard, which you can replace with the supplier’s value.

The gravel allowance is separate from the block cutting allowance. It multiplies both base and drainage stone volumes. Use a supplier-recommended allowance for compaction and handling; a percentage does not prove that the correct aggregate or compaction procedure has been selected.

Switching to metric changes the display units without changing the physical project. One foot is exactly 0.3048 metres, one inch is 25.4 millimetres, and one cubic yard is 0.764554857984 cubic metres. Metric weights are tonnes of 1,000 kg; imperial weights here are US short tons of 2,000 lb.

Plan pipe, fabric, and adhesive as separate line items

Pipe length is wall run plus the outlet allowance you enter. The roll count rounds that length up to your selected roll size. Elbows, tees, cleanouts, additional outlets, solid outlet pipe, sleeves, and fittings need a separate schedule. A length estimate does not establish that a drain has an appropriate route or lawful discharge point.

The geotextile allowance estimates one rear vertical face and one bottom strip of the drainage zone, plus the overlap percentage you enter. It does not specify a full enclosure or approve fabric placement. Check the design and soil compatibility before ordering a particular fabric; drainage filter fabric and reinforcing geogrid serve different purposes.

Adhesive quantity is based on the total bead length, the number of beads, and the coverage per tube that you enter. Coverage varies with bead diameter, tube size, surface texture, and the selected product. Check the tube label and the block supplier’s capping instructions instead of treating “one tube per fixed number of caps” as a universal rule.

A complete worked example: 30 feet × 3 feet

Start with a 30-foot straight wall and 3 feet of exposed block height. Choose 16-inch-long by 6-inch-high units, one buried course, and 10% block waste. There are ceil(360 ÷ 16) = 23 units per course, six exposed courses, and seven courses including the buried row.

The net count is 23 × 7 = 161 units. Of these, 138 are exposed and 23 are buried. Applying 10% allowance gives ceil(161 × 1.10) = 178 units to order. With an entered 75 units per pallet, that means three whole pallets if the supplier only sells full pallets. The calculator’s unit-price cost is still based on 178 units, so ask whether pallet-only purchasing changes your invoice.

With a 22-inch-wide base trench and 6 inches of compacted base depth, net base volume is 30 × (22 ÷ 12) × 0.5 ÷ 27 = 1.02 yd³. A 12-inch drainage zone behind the constructed 3.5-foot block height, less a 6-inch soil cap, adds 3.33 yd³. A 10% stone allowance produces about 4.79 yd³ in total, excluding hollow-core fill. At the illustrative density, that is about 6.70 US tons.

At 16 inches per cap, the net count is 23 caps and the order quantity is 26 after waste. Pipe is 34 feet with the default 4-foot outlet allowance. Change any input to match your product or plans and print the revised takeoff for your supplier.

Use local quotes to build the budget

The Costs tab contains example prices, not a live price feed or a national market average. Replace unit prices with written quotes for the exact units, cap stones, aggregate, pipe, fabric, adhesive, and any specified reinforcement. Enter delivery separately. Unit prices should use the selected display currency; changing the currency label does not convert money at an exchange rate.

Labor is calculated from the entered rate per exposed face area. It is a budgeting input rather than an installer quote. Tax is applied only to materials plus delivery in this model; actual tax treatment may differ. Excavation, spoil removal, permits, engineering, equipment, fittings, and site restoration are not included unless you budget for them separately.

Use the result as a consistent starting quantity list. Ask the supplier to verify package sizes, availability, curved-wall compatibility, special units, and minimum orders. Ask a qualified local professional to verify the design, drainage, ground conditions, and any permit requirements before construction.