Retaining Wall Block Calculator

The formula

Coverage and yield assumptions

Defaults describe a common small garden block about 12 in long and 4 in high. Larger commercial units may be 16–18 in long and 6–8 in high. The Concrete Masonry & Hardscapes Association recommends burying the first course; a common rule is 1 in of embedment per 8 in of wall height, with a 6 in minimum.

Base and drainage

Dig a trench wide enough for the block plus 12 in behind it and deep enough for 6 in of compacted gravel base plus the buried course. Level the base carefully: the first course sets the line for the whole wall. Behind the wall, place at least 12 in of clean drainage stone and a perforated drain pipe at the base that exits to daylight. Water pressure is the main reason small walls fail.

Height limits and permits

Many jurisdictions require a permit and an engineered design for retaining walls over 4 ft, measured from the bottom of the footing, or for walls with a surcharge such as a driveway or slope above. Taller walls usually need geogrid reinforcement layers that extend back into the soil. Terraced walls are an option for steep slopes; space them at least twice the height of the lower wall apart.

Curves and corners

Tapered blocks make curves easy; inside curves need fewer blocks per course and outside curves slightly more. Corners need special corner units or cut blocks. Steps can be built from wall blocks with caps as treads.

Building tips

• Call 811 before digging.
• Stagger vertical joints by at least a third of a block.
• Fill block cores and the area behind with clean stone as you go.
• Glue caps with masonry adhesive.

Common mistakes to avoid

• Skipping the buried course.
• Using soil instead of clean stone behind the wall.
• Building on an uncompacted or unlevel base.
• Exceeding height limits without engineering or geogrid.
• Forgetting a drain pipe at the base of taller walls.

Waste factor

5% covers chipped blocks and cuts on straight walls. Use 10% for walls with curves, steps or corners where blocks must be split.

Imperial and metric

Switch the toggle above the inputs to enter ft ↔ m, in ↔ cm. The page converts metric entries to imperial before calculating, using NIST factors (1 ft = 0.3048 m, 1 in = 2.54 cm), and shows key results in both systems.

Worked examples

Garden wall 30 × 3 ft

Inputs: wall length 30 ft; exposed wall height 3 ft; block face length 12 in; block height 4 in; cap length 12 in; buried courses 1; waste factor 5%.

Result: You need 315 wall blocks and 32 caps.

• Units to buy (rounded up): 315 blocks
• Blocks per course: 30
• Courses incl. buried: 10

Patio wall with larger units

Inputs: wall length 40 ft; exposed wall height 2.5 ft; block face length 16 in; block height 6 in; cap length 16 in; buried courses 1; waste factor 5%; cost per unit $4.6.

Result: You need 189 wall blocks and 32 caps.

• Units to buy (rounded up): 189 blocks
• Blocks per course: 30
• Courses incl. buried: 6
• Estimated material cost: $869.40

Raised bed border

Inputs: wall length 24 ft; exposed wall height 1 ft; block face length 12 in; block height 4 in; cap length 12 in; buried courses 0; waste factor 10%.

Result: You need 80 wall blocks and 27 caps.

• Units to buy (rounded up): 80 blocks
• Blocks per course: 24
• Courses incl. buried: 3

Quick reference for common sizes

The table repeats the first worked example at smaller and larger sizes, keeping every other setting the same, so you can see how the retaining wall block calculator result scales.

Limitations

Counts are for a straight wall of uniform height. Stepped bases, curves and corners change the count. Walls over 4 ft or carrying a load need professional design.