When looking at the box, the first number from left to right will usually be the gauge of the shells. The next number will be the length of the shell; this is important because shotguns can vary in their chamber size. After gauge and length, the next number listed is the weight of the shot in the round, followed by the size of the shot.
Finally, there is information on the velocity of the projectile at the point it leaves the barrel. This information might be listed in feet per second (FPS) or in the dram equivalent. Typically abbreviated as “Dr. Eq.,” the dram equivalent harkens to a time when black powder was used for firearms. Back then, black powder was measured in volume or “drams.” Some will forgo this listing in favor of “max” or “mag” to indicate it’s at the highest end of the spectrum.
The order can vary slightly, but each box will have this same information.