"J'ai grossi alors mon pantalon est trop serré."

Translation: I gained weight, so my pants are too tight.

[laurenmastinc]

I said "I got fatter" but I guess that was too blunt

[b_adger]

"got fatter" or "got bigger" or "have grown" are more accurate translations of "grossir". Gained weight is "prendre du poids" in French, although it is often used as a euphemism for getting fatter/bigger in English.

[jessArdeche]

I wouldn't say "I gained weight", I think "I have gained weight" sounds more natural

[Klgregonis]

I have gained weight is accepted.

[JennyRusse1]

I agree.

[MatthewBer6]

A vision I didn't need.

[skymmatt]

I said “I’ve grown” because I didn’t think to say got fatter or gained wait.
I would say “my bellies grown so much my trousers don’t fit”

[b_adger]

It could be that your thighs have grown from working out or cycling - this is my main problem with trouser fit.

[Brokleen]

Why 'mon pantalon' is mean 'my pants'?

[Klgregonis]

The word pants is an obligatory plural in most, if not all dialects of English. The only exceptions I can think of are some types of East Indian English. It is not an obligatory plural in French.

[b_adger]

"I have got bigger so my trousers are too tight", "I have got fatter so my trousers are too tight ", "I got fatter so my trousers are too tight", "I got bigger so my trousers are too tight", "I have grown so my trousers are too tight", "I am fatter so my trousers are too tight", "I am bigger, so my trousers are too tight" were not accepted - reported.