It covers the tambon Nai Mueang of the Phetchabun District, along the Pa Sak River.

The Pa Sak River runs through the east side of Phetchabun from north to south.

The town lies in a valley; the two ranges of the Phetchabun Mountains rise to both the east and west.

The monsoon season runs from late April through early October, with heavy rain and somewhat cooler temperatures during the day, with nights remaining warm.

The main road through the city is Route 21, from Lom Sak to the south through Phetchabun to Chai Badan and Saraburi.