It doesn't increase poise by a flat amount, it has weird scaling and poise appears to have diminishing returns.
With no armour on it increases poise by 45, but (initially says it will increase it by 69.75.)
With no armour and Wolf Ring +1 it increases poise from 17.50 to 54.62, an increase of about 37 (initially saying it will increase it to 75.04)
With full Artorias/Wolf Knight armour and Wolf Knight Ring +1 it increase poise from 31.62 to 62.39, an increase of 31. (initially saying it will increase to 79.31)
Without the ring, Yhorm's shield increases poise from 17.11 to 54.41 an increase of about 37. (initially saying it will increase to 74.93)
At 0 poise you get 45, but as your poise increases that amount goes down. Before equipping it might be bugged as it never shows how much poise you will actually have and is much greater than 45, or whatever bonus you do get.