How Many Blocks for a 20 ft Retaining Wall, 2 ft High?

A 20 ft long wall standing 2 ft above the ground needs 79 blocks in the standard 16 × 6 in size, counting one buried course and 5% extra, plus 20 caps and about 4.2 tons of gravel for the base and drainage. At typical US prices the materials cost about $613–$1,170.

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How it's worked out

  1. Blocks per course: 20 ft × 12 = 240 in ÷ 16 in = 15 (rounded up)
  2. Courses: 2 ft × 12 = 24 in ÷ 6 in = 4, plus 1 buried course = 5
  3. Blocks: 15 × 5 = 75, plus 5% for breakage = 79
  4. Caps: 240 in ÷ 12 in caps = 20
  5. Base gravel: 24 in wide × 6 in deep trench, +15% for compaction = 1.2 tons
  6. Drainage gravel: 12 in behind the wall for its full 2.5 ft, +15% = 3 tons

20x2 wall with other block sizes

Block faceTypeBlocksBlock priceMaterials cost
12 × 4 inSmall garden block147$2–$3.5 each$543–$1,034
12 × 6 inMedium block105$3–$5 each$573–$1,063
16 × 6 inStandard wall block79$4.5–$8 each$613–$1,170
18 × 6 inLarge wall block74$6–$12 each$702–$1,426

Materials cost covers blocks, 20 caps at $3–$7 each, base and drainage gravel at $40–$75 a ton in bulk, and 20 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 a lot of blocks; it's often cheaper than buying them one at a time.

A 2 ft wall is a comfortable DIY size for most segmental blocks. Spend most of your effort on a level, compacted base and good drainage behind the wall.

Other common sizes

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