I rewrite here a full explanaton Noi diciamo: a) fetta di pane (slice) b) pezzo di pane (from a big loaf) c) panino, with two meanings: m1: sandwich, m2: small 'piece of bread' that is not cut from a bigger one Very seldom we say 'pani'. We say : ho mangiato del pane Ho mangiato cinque fette di pane duro: correct. Note that unless you use 'panino, panini' pane always wants either /del/, or a measure word like {pezzo di , fetta di, un po' di }, this is why we use it at singular. Pezzi di pane, NON: pezzi di pani.

The word is "panino". Ho mangiato cinque panini (piccoli). slice of bread = fetta di pane ps: you can't say " 5 breads", "bread" is an uncountable noun.