Nouns ending in -it or -ut are masculine.
The whole family: -it, -ut. All masculine.
Is petit masculine or feminine?
lepetit
The feminine form is petite
The rule behind it
100% of -it / -ut nouns are masculine
In context
Non, c'est pas mon nouveau petit ami.
No, he's not my new boyfriend.
Je viens juste de finir mon petit déjeuner.
I've just finished breakfast.
Mes pieds sont plus petits que les tiens.
My feet are smaller than yours.