Segmental wall blocks stack in courses, so this view reports both the block count and the number of courses. Get the base course dead level — every course above inherits its errors, and walls over 3–4 feet usually need an engineer.
Field notes
The base course is the whole wall — spend your time leveling the gravel pad, because every course above copies its errors. Bury the first course at least one block-height below grade so the wall can't kick out at the bottom. The calculator sizes a base one block wider than the wall and 6 inches deep for exactly this reason. Anything over 3–4 feet usually needs an engineer and a permit; check locally before you dig.
How the retaining wall blocks calculator works
The math behind the tool:
blocks = (wall length ÷ block width) × (wall height ÷ block height)Sources: Concrete Masonry & Hardscapes Association (segmental retaining wall installation (formerly ICPI/NCMA)).