A blade grinder has no gap to grind to, so the only thing deciding the size is how well the beans circulate past the blade — and that is governed by how many BEANS DEEP the pile is, not by how many grams are in it. One or two beans deep circulates; five is a wall.
A struck bean has to fight out through the beans above it, and bean-on-bean restitution is about 0.35, so a bounce returns an eighth of the height and four layers absorb over 99% of a strike. Beans near the blade then get hit over and over while the ones on top wait their turn, and because grinding follows Bond’s law — the last halving costs far more than the first — a moderately uneven strike count becomes a wildly uneven grind. That is why blade coffee tastes sour and bitter at the same time: the dust over-extracts while the boulders barely extract at all.
Depth, not grams: the same 40 g is three beans deep in a narrow pot and one and a half in a wide one, so the useful move is often a wider chamber rather than less coffee. The damage also arrives early and then plateaus — the spread widens most over the first two or three bean-layers and barely worsens after that, so halving an already deep batch buys much less than keeping a shallow one shallow. And none of it applies to a burr grinder, which has an actual gap.
Estimate with the rule, then check it against the calculator that models it properly.
Open Coffee Grinder Simulator →A blade grinder has no gap to grind to, so the only thing deciding the size is how well the beans circulate past the blade — and that is governed by how many BEANS DEEP the pile is, not by how many grams are in it. One or two beans deep circulates; five is a wall. A struck bean has to fight out through the beans above it, and bean-on-bean restitution is about 0.35, so a bounce returns an eighth of the height and four layers absorb over 99% of a strike.