Se mettre sur son trente et un


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Informal French Expression

Meaning	to get dressed up, dolled up; to put on one’s Sunday best
Literally	to put on one’s thirty-one
Register	informal
Pronunciation
	[seu me tr(eu) sur so(n) tra(n) tay oo(n)]
IPA	[sə mɛtrə syr sɔ̃ trã te œ̃]

Usage notes: In English, a truly beautiful person is a "perfect 10." But since the French are just so much more chic and sophisticated, their scale goes up to 31! 😉 The expression se mettre sur son trente et un (to get dressed up) and its synonym être sur son trente et un (to be dressed up) use this unusual number to indicate elegant or special clothing. Alain Rey posits in Dictionnaire historique de la langue française that it could be

et je cite

une allusion portant sur le jour excédant le compte des jours d’un mois normal (de trente jours)

In other words, if you get all dressed up on the 31st day, it’s automatically special because that works out to less than once a month.

Par exemple…

Sortons en boîte ! Allez, mets-toi sur ton ton trente et un !		Let’s go to a club! Come on, go get dolled up!
Marie-Claude est très chic, elle est toujours sur son trente et un.		Marie-Claude is very chic, she’s always dressed to the nines.

Interestingly, the expression was originally se mettre sur son trente-six, which brings it closer to English’s "perfect 10." Trente-six indicated nine out of ten times four; in other words, “very nice times four." (There are quite a few French expressions with trente-six – see the list at the end of tous les 36 du mois).

Synonymous expressions