What do you mean exactly "for each one"?  Each value, on it's own, doesn't tell you enough. You can't validate that the weight of the item per cubic inch is above the threshold unless you have know the length, width and height (volume) and the weight of the parcel.

As an example:
I have a parcel measuring 10'' x 6'' x 3''.  Is it too heavy?
I also have a parcel weighing 60lbs. It is 4'' wide and 6'' high. Is it too heavy?

You don't know, as you don't know the weight or length of the parcel. (respectively). If, however, I added the final piece of the puzzle:
I have a parcel measuring 10'' x 6'' x 3''. It weight 100lbs.  Is it too heavy? - Yes, it weighs 0.27~lbs per square inch.
I also have a parcel weighing 60lbs. It is 4'' wide, 6'' high and 10'' long. Is it too heavy? - No, it weighs exactly 0.25 lbs per square inch.

Only when I add the final piece of the puzzle can you CHECK.