Increases your hit points by +3 at first level, and 1 additional hit point for each additional level.
Notes
Total of 36 hit points at level 34 (<level> + 2 hitpoints in total). This is very slightly better than a +2 bonus to Constitution, which would provide exactly <level> hit points.
This feat can be taken multiple times, and the effects stack.
The formula for extra hit points is based on character level, the level where the Toughness feat has been gained does not change anything.
Having multiple Toughness feats while having Epic Toughness when doing a respec of Toughness, requires Epic Toughness to be respec first followed by the Toughness feat.