Nephin is a Hewitt of 806 m in Mayo. Nothing higher stands within 51.7 km; the nearest higher summit is Mweelrea (814.5 m), to the south-west.
In the database's Nephin Beg Range region it is the highest of five register hills, above Slieve Carr and three others. The key col lies 22.3 km away to the south, at 38 m. Its closest neighbour in this register, Birreencorragh, is 8.4 km away. Its drop is the 9th greatest among the Hewitts, behind Snowdon – Yr Wyddfa at the top. Its drop of 768 m is 95% of its height: the col linking it to higher ground is only 38 m above sea level. It overtops all four of its nearest neighbours; the tallest of them, Slieve Carr, reaches 721 m. Of the register hills in Mayo, only Mweelrea stands higher. All four of its nearest neighbours lie to the west, so it stands at the eastern edge of its group. The summit is marked by a trig point.
