Retaining Wall Calculator
Calculate blocks, backfill gravel, drain pipe, and total cost for your retaining wall project.
How to Use This Calculator
Planning and Estimating a Retaining Wall Project
Retaining walls are essential for managing slopes, preventing erosion, and creating level terraces in landscaping. Proper material estimation is critical since retaining wall blocks are heavy (30-80 lbs each) and delivery logistics require accurate quantities.
The most common retaining wall materials are interlocking concrete blocks, natural stone, timber, and poured concrete. Interlocking blocks are the most popular DIY option because they require no mortar and stack easily with built-in lip or pin alignment systems.
Standard retaining wall blocks are approximately 12 inches wide × 4 inches tall × 8 inches deep. At this size, you need about 3 blocks per linear foot per course (row). A 4-foot tall wall has 12 courses and requires 36 blocks per linear foot of wall length.
Backfill material is often overlooked in cost estimates. You need drainage gravel behind the wall (at least 12 inches deep), landscape fabric to prevent soil migration, and a perforated drain pipe at the base. These materials typically add 25-40% to block costs.
Walls over 4 feet tall usually require engineering and permits. Taller walls experience significantly more lateral earth pressure, requiring geogrid reinforcement, deeper bases, and potentially battered (tilted back) designs. Always consult local codes before starting.
Frequently Asked Questions
How many blocks do I need for a retaining wall?
Multiply wall length (in feet) by wall height (in feet), then multiply by approximately 9 blocks per square foot for standard-size blocks. A 20-foot long, 3-foot tall wall needs about 540 blocks plus 10% waste (594 blocks total).
How much does a retaining wall cost per foot?
DIY retaining walls cost $10-$25 per square foot of wall face for materials. Professional installation runs $25-$50 per square foot. A 20-foot long, 3-foot tall wall costs $600-$1,500 DIY or $1,500-$3,000 professionally installed.
Do I need a permit for a retaining wall?
Most jurisdictions require permits for retaining walls over 4 feet tall (measured from the bottom of the footing to the top of the wall). Some areas require permits for walls over 3 feet. Walls holding surcharges (driveways, structures) may have stricter requirements.
How deep should the base be for a retaining wall?
Bury the first course 1-2 inches below grade. The gravel base should be 6 inches deep and extend 2-3 inches beyond the front and back of the blocks. Compact the base thoroughly to prevent settling.