Where many standing stones are tall and narrow, this one is almost the opposite: broad, flat-topped, and considerably wider than it is tall. The dimensions recorded by P. J. Hartnett in 1939 make the proportions plain enough, at roughly 34 inches high but 72 inches wide and only 10 inches thick. It is less a pillar than a slab held upright, closer in feel to a large stone tablet than the tapered monoliths more commonly associated with prehistoric monuments.

Hartnett's 1939 account remains the primary description of the stone. Standing stones of this kind are among the most difficult prehistoric monuments to date with any precision; they were erected across a broad span of prehistory, most commonly during the Bronze Age, and served purposes that are still debated, ranging from territorial markers to sites of ritual significance or astronomical alignment. What distinguishes the Knocknagoun example is simply its form. That squat, wide profile, with a flattened top rather than a pointed apex, sets it apart from the taller, more slender examples that tend to draw more attention elsewhere in Cork and across Ireland generally. The stone was recorded as removed at some point after Hartnett's visit, which means the description from 1939 may represent the last detailed account of it in situ.