Fan Gyhirych is a mountain in the Fforest Fawr section of Brecon Beacons National Park in south Wales. It lies within the county of Breconshire, and administered as part of the unitary authority of Powys. Its highest point at 2379 feet (or 725 m) is marked by a trig point which is located towards the western side of the summit plateau. The hill drains to the north into the catchment of the Afon Crai and to the south and west into that of the River Tawe. Fan Fraith is a nearby hill which can be considered a subsidiary top of Fan Gyhirych.