Plan your project in a couple of minutes. Enter your measurements below and the retaining wall calculator shows you exactly what you need to get started. Still choosing a system? Browse our retaining wall blocks first. Building a patio or driveway too? Use the paving stone calculator.
These numbers are a planning estimate, not an engineered design. For a wall under 4 feet, take this list to a local dealer and build it yourself. Walls over 4 feet usually need an engineered design, a permit, and soil reinforcement behind the wall, so have a certified installer review the project before you buy anything.
This calculator does not include geogrid, drain pipe, filter fabric, construction adhesive, corner units, or pricing of any kind. Reinforcement in particular depends on your soil, what sits above the wall, and how the wall is battered, which makes it an engineered value rather than a formula.
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To calculate how much retaining wall you need, multiply wall length by wall height to get the face area, then divide that by the face area of one block. A 6 by 16 inch block covers 0.67 square feet, so a 24 foot wall standing 3 feet tall is 72 square feet of face and roughly 119 blocks once you add waste.
The number of blocks you need is the wall face area divided by the face area of one block, plus a waste allowance. Divide wall length by block width for blocks per row, divide wall height by block height for the number of rows, multiply the two, and add 10 percent. The calculator above does all of it from two measurements.
The gravel behind a retaining wall fills a drainage zone roughly 12 inches deep, running the full length and height of the wall. For a 24 foot by 3 foot wall that is about 2.9 cubic yards, or 4.1 tons of crushed stone. Use 3/4 inch clean angular stone with no fines so water can move through it freely.
A 4 foot retaining wall needs a trench roughly 12 inches deep: 6 inches of compacted base stone plus one full buried block course sitting on top of it. The trench should be about 2 feet wide so the base extends past both faces of the block. Soft or wet soils need more, which is one of the things an installer checks on site.
The 1/3 rule is a rough guideline used two different ways, either that the footing should sit at a depth of about one third the wall height, or that the base should be about one third as wide as the wall is tall. Neither version governs modern segmental block walls, which are built to the manufacturer’s tables and, above 4 feet, to an engineered design. For a Nicolock wall, bury one full course and set it on 6 inches of compacted base.
Most jurisdictions allow a segmental block retaining wall up to 4 feet without an engineered design or a permit, measured from the bottom of the buried course. Above 4 feet you generally need a stamped design, a permit, and geogrid reinforcement. Check your local building department, because the threshold varies and some towns set it lower.
Nicolock wall blocks come in three face sizes. Alta Wall and Firma Wall use a 6 by 16 inch face and handle most residential retaining walls, while Alta Pro and Keystone Compac III use an 8 by 18 inch face that covers more area per unit for taller or longer runs. Stonegate uses a 6 by 10 inch face built for seat walls and garden borders rather than heavy earth retention.
Every wall also needs wall caps to finish the top and shed water. Outcropping Wall and 6 inch Colonial Wall are not sized for counting by the piece, so use the wall face area figure above and let your dealer convert it to pallets. All of our wall blocks are made in our own U.S. plants with color running through the entire unit, and they carry a transferable lifetime warranty.
The cost of a 100 foot retaining wall depends far more on height than length, because height drives block count, base and drainage volume, and whether the wall needs an engineered design and a permit. Block choice, site access, excavation, and local labor rates set the rest. Run the calculator for your quantities, then take that list to a dealer or a certified contractor for real pricing in your market.
