Retaining Wall Calculator
Find how many blocks and cap blocks a retaining wall needs, plus base and backfill gravel, with cost.
Change the values and press Calculate to work out your own figures.
Enter the wall's length and height and the block size.
Show the working
- columns = ⌈wall length ÷ block width⌉; rows = ⌈wall height ÷ block height⌉ (one fewer under a cap row)
How to use it
Enter the wall's length and height and the block size.
Lengths can be decimals, fractions or tape entries such as 12' 6 1/2" (in feet or inches). Prices are optional.
Key facts
blocks = ⌈wall length ÷ block width⌉ × ⌈wall height ÷ block height⌉ (one fewer row under a cap row) base gravel = 2 × block depth × wall length × 6 in; backfill = 12 in × wall length × wall height
Safety
Walls over about 4 ft, or holding back a slope, a driveway or a building, usually need an engineer's design and a permit; check your local code.
Questions
How many blocks for a 30 × 3 ft wall of 10 × 6 in blocks?
216 blocks (6 rows of 36).
Formulas
blocks = ⌈wall length ÷ block width⌉ × ⌈wall height ÷ block height⌉ (one fewer row under a cap row) base gravel = 2 × block depth × wall length × 6 in; backfill = 12 in × wall length × wall height
Sources
Limitations
- Material densities are typical values (the midpoint of the commonly published range); real loads vary with moisture, grading and compaction, so check with your supplier or type in their density.
- Tank results are the geometric volume; real tanks have wall thickness and fittings.