Om3gA's page

Just as if the Barbarian had gained a higher Con score through other means (such as a magic item or a bonus every 4 levels), his total Con bonus to HP is equal to his HD x Con modifier. Since a +4 bonus to Constitution will increase the barbarian's modifier by +2, he gains an additional two hit points per Hit Dice. So a 20th level barbarian, when raging gains an effective +40 to his hp total.

Thank you very much m8

This is probably so simple i'll feel like a moron for asking however to me its just not worded clear.

The rules state...

....to her Strength and Constitution, as well as a +2 morale
bonus on Will saves. In addition, she takes a –2 penalty
to Armor Class. The increase to Constitution grants the
barbarian 2 hit points per Hit Dice, but these disappear
when the rage ends and are not lost first like temporary
hit points.

Rather than state how i'm reading it which i know is totally wrong, i'll simply ask for someone to explain it to me. And I have already gotten mixed answers via google which is rather annoying, for the curious the numbers i've seen are 40 80 and 480 max hp bonus at lvl 20. Please and thank you in advance.