Retaining wall calculator
Enter the wall's length and height and the block size. You get the courses, the blocks and caps to order, and the gravel for the base and the drainage zone, laid out the way the block industry's guide shows.
Inputs
Result
| Item | Order |
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How it is worked out
A 30 ft wall 2 ft high in 12 x 4 in blocks is six exposed courses and one buried: seven courses of 30 blocks, 221 with 5% waste, plus 32 caps. The 6 in leveling pad is 25 in wide (6 in in front, the 7 in block, 12 in behind): 1.2 cubic yards of compactable base. The 12 in drainage zone behind the full 28 in of wall is 2.6 yards of clean stone.
Base and drainage
The National Concrete Masonry Association's installation guide puts the first course on a compacted leveling pad at least 6 in thick, running from 6 in in front of the blocks to 12 in behind them. Behind the wall, clean gravel at least 12 in wide runs the full height, with a perforated drain pipe at the bottom where water needs to get out. Water pressure behind a wall that cannot drain is what pushes most small walls over.
Questions
How many retaining wall blocks do I need?
Work out the courses from the height and block height, adding at least one buried course, then multiply by the blocks per course: wall length in inches over block length. A 30 ft wall 2 ft high in 12 x 4 in blocks takes 210 blocks, 221 with waste.
How deep should the gravel base be for a retaining wall?
At least 6 in of compacted base, extending 6 in in front of the blocks and 12 in behind them, per the NCMA installation guide. More on soft ground.
How much gravel goes behind a retaining wall?
A zone of clean drainage stone at least 12 in wide for the full height of the wall. For a 30 ft wall 28 in tall that is about 2.6 cubic yards.
How tall can a retaining wall be without an engineer?
Under the IRC, 48 in of retained soil, if nothing else loads it. Most block makers set lower limits for walls without geogrid, so check your block's chart.
How many retaining wall blocks are in a pallet?
It varies by block: small 12 in wall blocks often come 100 to 150 to a pallet and large blocks 40 to 60. The pallet label or dealer will tell you.
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