Retaining Wall Calculator
Find out how many concrete blocks you need for a retaining wall - enter the wall length and height and pick your block size.
How to use this retaining wall calculator
Measure the length of the wall and the planned height in feet. For a wall taller than 4 feet, you should have a structural engineer check the design - most building codes require it.
Pick your block size. The face area per block determines the count: a standard 8x16 in block covers 0.89 sq ft of wall face, a 6x16 in block 0.67 sq ft, and a 4x16 in block 0.44 sq ft (including mortar joints).
Add 5% waste for a straight wall, or 10% if there are curves or corners to cut. Order caps separately - one cap block per foot of wall length for most styles.
Retaining wall calculator FAQ
How many blocks do I need for a 50-foot wall?
A 50 ft long, 3 ft high wall has 150 sq ft of face area. With standard 8x16 in blocks (0.89 sq ft each) and 5% waste, that is about 177 blocks - roughly 9 rows of 20.
How tall can a retaining wall be without engineering?
Most codes allow up to 3-4 feet (the height of one or two block courses plus footing) without an engineer. Above that, walls are typically designed with geogrid reinforcement, deeper footings and drainage.
Do retaining walls need drainage?
Yes - install a gravel base and perforated pipe behind the wall, or water pressure will push it over. Plan about 1-1.5 tons of drain gravel per 10 feet of wall length for a 3-foot wall.