Piatto is a comune (municipality) in the Province of Biella in the Italian region Piedmont, located about northeast of Turin and about northwest of Biella. On 31 December 2004, it had a population of 527 and an area of .
Piatto borders the municipalities of Bioglio, Callabiana, Camandona, Mosso, Quaregna, Ternengo, Valdengo, Vallanzengo, Valle San Nicolao and Veglio.