Blackstairs Mountain is a Hewitt of 732.1 m in Carlow, Wexford. Its drop of 537 m is 73% of its height: the col linking it to higher ground is only 195 m above sea level.
It is one of only three register hills in the Waterford, Kilkenny, Carlow region, with Mount Leinster and Slievenamon. All four of its nearest neighbours lie to the north, so it stands at the southern edge of its group. It shares its height of 732.1 m with Beinn na Caillich (Highland, NG601232). The highest point is recorded as peat hag, not a cairn.