Round down, always
If two and a half totes fit across a level, two totes fit. Partial totes do not exist, and the leftover space is not usable capacity.
This is why capacity should be computed from exact measurements rather than from rounded display values — a number that rounds up on screen can round a whole tote out of the answer.
Verify each level separately
Levels in the same unit are frequently not identical. The bottom level often sits on a different foot height, the top level is often limited by the frame, and any level can have been moved.
Count only the levels you have measured and confirmed will take the tote. An unverified level is not capacity.
Capacity is geometry, not load
How many totes fit is a separate question from how much weight the shelf can carry. Shelving carries a manufacturer load rating per level, and full totes are heavy.
Check the rating for your unit before filling every level you can geometrically fill.
Check your own measurements
Get an exact capacity count — the calculator runs entirely in your browser and stores nothing.