Birks reaches a height of 622 metres (2,041 feet) and is characterised by a grassy summit ridge which has precipitous craggy slopes to the north and west which fall away to the valley of Grisedale, its southern flank is steep and grassy and ends in the valley of Deepdale and to the north east the main ridge descends towards Patterdale over Black Crag and through Glenamara Park.

Birks is regarded by guide book writers as an unspectacular fell, it has 19 metres (62 ft) of prominence from St Sunday Crag and therefore qualifies as a Nuttall, while Alfred Wainwright gives the fell a separate chapter in his Pictorial Guide to the Lakeland Fells because "it is sufficiently well defined to deserve a separate name".

The principal rocks of the summit area are the pebbly sandstones of the Blind Cove Member.

The ascent is a pleasant walk through the wooded Glenamara Park along a footpath which leaves Patterdale and follows Hag Beck and then a ruined dry stone wall to the summit.

An alternative route goes via Thornhow End and finds a way through Black Crags at attain the top of the fell.