Retaining Wall Calculator
Plan your civil engineering project with our free retaining wall calculator. Get precise measurements, material lists, and budgets.
Formula
Wall Volume = Height x Length x Thickness | Footing Volume = Width x Length x Depth
The concrete volume for a retaining wall is calculated by determining the wall stem volume (height times length times thickness) and the footing volume (width times length times depth) separately, then adding them together. Rebar quantities are estimated based on vertical bar spacing (typically 16 inches on center) and horizontal bar spacing (typically 24 inches on center).
Worked Examples
Example 1: Standard 6-Foot Retaining Wall
Problem: Calculate materials for a 50 ft long, 6 ft tall retaining wall with 12-inch thickness, 4 ft wide footing, and 12-inch deep footing.
Solution: Wall volume = 6 x 50 x 1 = 300 cu ft = 11.11 cu yd\nFooting volume = 4 x 50 x 1 = 200 cu ft = 7.41 cu yd\nTotal concrete = 18.52 cu yd\nVertical rebar (16 in OC): 38 bars\nHorizontal rebar (24 in OC): 4 rows
Result: 18.52 cu yd concrete, 38 vertical bars, 4 horizontal rows
Example 2: Garden Retaining Wall
Problem: Calculate concrete for a 20 ft long, 3 ft tall wall with 8-inch thickness and 2.5 ft wide, 10-inch deep footing.
Solution: Wall volume = 3 x 20 x 0.667 = 40 cu ft = 1.48 cu yd\nFooting volume = 2.5 x 20 x 0.833 = 41.67 cu ft = 1.54 cu yd\nTotal concrete = 3.02 cu yd
Result: 3.02 cu yd total concrete needed
Frequently Asked Questions
How thick should a concrete retaining wall be?
The thickness of a concrete retaining wall depends on its height and the lateral earth pressure it must resist. A general rule of thumb is that the wall thickness at the base should be at least 8 inches for walls up to 4 feet tall and 10 to 12 inches for walls 4 to 8 feet tall. Walls taller than 8 feet typically require engineering design and may need a tapered cross-section that is thicker at the base and thinner at the top. Reinforced concrete walls can be thinner than unreinforced gravity walls.
How wide should the footing be for a retaining wall?
The footing width for a retaining wall is typically 50 to 70 percent of the total wall height. For a 6-foot retaining wall, the footing should be approximately 3 to 4 feet wide. The footing extends behind the wall (toward the retained soil) to resist overturning and should be deep enough to reach below the frost line, typically 12 to 18 inches thick. A key (a notch in the bottom of the footing) helps resist sliding and is usually 4 to 6 inches deep.
What rebar is needed for a retaining wall?
Typical reinforced concrete retaining walls use number 4 or number 5 rebar. Vertical bars are placed on the tension side (soil side) at 12 to 16 inches on center and extend from the footing through the full wall height with proper development length. Horizontal bars are placed at 18 to 24 inches on center to resist temperature and shrinkage cracking. The footing requires both top and bottom reinforcement running in both directions, typically number 4 bars at 12 inches on center.
Do all retaining walls need a footing?
Most retaining walls over 2 to 3 feet in height require a footing or foundation to distribute loads and prevent settlement, sliding, and overturning. Gravity walls made from large stone or concrete blocks may not need a poured footing if they sit on a compacted gravel base, but they still need a level and stable foundation. Segmental retaining walls use a compacted aggregate leveling pad instead of a concrete footing. Only small garden-type walls under 2 feet typically work without any footing.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.