How Many Blocks for a 30 ft Retaining Wall, 3 ft High?

A 30 ft long wall standing 3 ft above the ground needs 170 blocks in the standard 16 × 6 in size, counting one buried course and 5% extra, plus 30 caps and about 8 tons of gravel for the base and drainage. At typical US prices the materials cost about $1,232–$2,328.

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How it's worked out

  1. Blocks per course: 30 ft × 12 = 360 in ÷ 16 in = 23 (rounded up)
  2. Courses: 3 ft × 12 = 36 in ÷ 6 in = 6, plus 1 buried course = 7
  3. Blocks: 23 × 7 = 161, plus 5% for breakage = 170
  4. Caps: 360 in ÷ 12 in caps = 30
  5. Base gravel: 24 in wide × 6 in deep trench, +15% for compaction = 1.8 tons
  6. Drainage gravel: 12 in behind the wall for its full 3.5 ft, +15% = 6.3 tons

30x3 wall with other block sizes

Block faceTypeBlocksBlock priceMaterials cost
12 × 4 inSmall garden block315$2–$3.5 each$1,084–$2,043
12 × 6 inMedium block221$3–$5 each$1,130–$2,073
16 × 6 inStandard wall block170$4.5–$8 each$1,232–$2,328
18 × 6 inLarge wall block147$6–$12 each$1,349–$2,732

Materials cost covers blocks, 30 caps at $3–$7 each, base and drainage gravel at $40–$75 a ton in bulk, and 30 ft of 4 in perforated drain pipe. It leaves out tax, delivery, landscape fabric and tool rental. Ask for a pallet price if you need this many blocks; it's often cheaper than buying them one at a time.

At 3 ft high this wall is close to the limit for an unreinforced block wall. Above about 3 to 4 ft, or if it holds up a driveway or a steep slope, it usually needs geogrid, an engineer's design and a permit, so check with your town first.

Other common sizes

More detail: How Many Retaining Wall Blocks Do I Need? Charts by Wall Size