How this retaining wall calculator works
Blocks per row is the wall length divided by the face length of one block; rows is the wall height divided by block height, and the two multiply into the total. Cap blocks finish the top course — one per block position. The base figure covers a compacted gravel trench 12 inches (30 cm) wide and 6 inches (15 cm) deep under the wall, which is the standard footing for segmental block walls.
Bury the first course
The bottom row belongs below grade — bury roughly one tenth of the wall height, minimum one full course. That locks the wall against sliding. Each course above steps back slightly (the blocks' lip or setback does this automatically), leaning the wall into the slope it holds.
Know the height limit
Most garden-center blocks are rated for walls up to 3–4 ft (0.9–1.2 m) without engineering. Taller walls, walls holding driveways or slopes, and terraced walls closer together than twice their height need geogrid reinforcement and usually a permit — check local rules before building. Backfill behind the wall with clean gravel, not soil, so water drains instead of pushing.