Two thresholds
On this page13
Below 12 square inches
All information within the nutrition label is in type no smaller than 4.5 point. The smallest permitted setting, for the smallest packages.
From 12 to 40 square inches
No smaller than 6 point. A point and a half larger, across a band that covers a more than threefold range of area.
Above 40 square inches
The small and intermediate package provisions are not the governing ones, and the general type size rules for the panel apply instead. Those are not quoted on these pages.
Which means the bands are relief provisions
They exist to let a small package carry the panel at all. A larger container does not need relief and does not get these allowances.
So smaller is not simpler here
A small package gets a smaller permitted type and a harder layout. The relief is permission to shrink, not permission to omit.
The 12 square inch line is low
A cylinder 2 inches across and 2 inches tall has a side wall of about 12.6 square inches. So almost any jar clears it.
And none of our 147 measurable containers is below it
The smallest is 12.06 square inches on the side wall alone, which with the lid and base counted is comfortably over 12.
The 40 square inch line is the live one for us
91 of 147 containers sit in the 12 to 40 band on our side-wall figure and 56 are over 40.
Which makes it the boundary to check
A container our figure puts at 35 square inches may be over 40 in the regulation's own measure, because the regulation counts more surface than we do.
The bands are about the nutrition label specifically
The type size floors apply to all information within the nutrition label. Other required statements on the package have their own rules and are not quoted here.
So the panel and the rest of the label are budgeted separately
Which matters on a container near a boundary, because the panel may be entitled to shrink while the surrounding text is not.
Erring toward the smaller band is the safe direction
Designing to 6 point when you are entitled to more is permitted. The other way round is not.