Type size by panel area
On this page8
The bands
Up to 2 square inches: signal word 3/64 inch, hazard statement 3/64, other cautions 1/32. Over 2 and up to 5: 1/16, 3/64, 3/64. Over 5 and up to 10: 3/32, 1/16, 1/16.
And the larger panels
Over 10 and up to 15: 7/64, 3/32, 1/16. Over 15 and up to 30: 1/8, 3/32, 5/64. Over 30 square inches: 5/32, 7/64, 3/32.
Capital letter height, not point size
Two typefaces set at the same point size have different capital heights. Specifying 8 point to a designer does not establish compliance; measuring the printed capital does.
And a width limit as well
The letter height to width ratio may not exceed 3 to 1. A condensed face used to fit a long hazard statement into a narrow panel can breach that while every letter is still tall enough.
Capitals for the signal word and the hazard
Both are set in capital letters. That costs width, which interacts with the ratio limit and with the panel area, which is the usual reason a small bottle turns out to be the wrong bottle.
Work it from the panel, not the artwork
Measure the principal display panel of the container you intend to use, find the band, and set the three type sizes before any layout exists. The band changes at 2, 5, 10, 15 and 30 square inches, so a small change of container can move you a whole band.
A curved panel is smaller than it looks
On a cylindrical bottle, the principal display panel is what can be seen without turning the container. Measuring the full wrap and treating it as panel area overstates what you have, usually by enough to matter.