How the calculator works
Block walls are a grid: blocks per course = wall length ÷ block width, and courses = wall height ÷ block height, each rounded up, plus 5% for cuts and culls. Cap blocks run one per block-width of wall length. The gravel figures cover the two things every segmental wall needs: a 6″ compacted base one foot wide, and a 12″ column of clean drainage stone directly behind the blocks.
Worked example: a 30 ft wall, 2 ft tall, in 12×4″ blocks: 30 blocks per course × 6 courses = 180, plus 5% = 189 blocks, 30 caps, about 0.8 tons of base gravel and 3.1 tons of backfill stone.
The rules that keep walls standing
- Bury the first course at least 10% of the wall height below grade, on 6″ of compacted crushed base. Walls fail from the bottom.
- Drainage is not optional: clean angular stone behind the wall and a perforated drain pipe at the base outlet. Water pressure, not soil, is what topples walls.
- Setback: lipped blocks self-batter; keep the design lean into the slope.
- Know your limit: most municipalities require engineering above 3 or 4 ft of exposed height. Terraces of short walls beat one tall gamble.
Buying notes
Standard 12×4 blocks weigh 20–35 lb each, so 189 blocks is around 2.5 tons, so delivery beats twenty sedan trips. Blocks come on pallets; ask the yard for the per-pallet count and price break.