Nous sommes treize.

In French, être can be used with a number to say how many people are in a group.

So Nous sommes treize means There are thirteen of us or We are thirteen (people).

This is normal French, even though the most literal English version sounds a bit odd. French uses this pattern much more naturally than English does.

No. In this sentence, treize means the number of people, not age.

French age is expressed with avoir, not être:

• Nous avons treize ans = We are thirteen years old

So:

• Nous sommes treize = there are thirteen of us
• Nous avons treize ans = we are thirteen years old

French often leaves out personnes when the meaning is obvious.

So both are possible:

• Nous sommes treize
• Nous sommes treize personnes

The shorter version is very natural. Adding personnes just makes it more explicit.

Because the subject is nous, and être has to agree with the subject.

Present tense of être:

• je suis
• tu es
• il / elle / on est
• nous sommes
• vous êtes
• ils / elles sont

Since the sentence starts with nous, the correct form is sommes.

Nous is the subject pronoun, meaning we.

It tells you who the sentence is about. Then sommes matches that subject, and treize tells you the number.

So the structure is:

• Nous = we
• sommes = are
• treize = thirteen

No. Treize stays the same.

French cardinal numbers like un, deux, trois, treize usually do not change form here.

So whether the group is all male, all female, or mixed, you still say:

• Nous sommes treize

Yes. On est treize is very common in everyday spoken French.

It means the same thing as Nous sommes treize in this context.

The difference is mostly style:

• Nous sommes treize = a bit more formal or careful
• On est treize = very common in conversation

They are close, but not exactly the same.

• Nous sommes treize = There are thirteen of us / We are thirteen
• Il y a treize personnes = There are thirteen people

The first sentence includes the speaker as part of the group. The second just states how many people there are.

So if you are one of the thirteen, Nous sommes treize is the natural choice.

Yes, absolutely.

• Nous sommes treize = natural and concise
• Nous sommes treize personnes = clearer, a bit more explicit

French often prefers the shorter version when the noun is easy to understand from context.

It is pronounced approximately:

noo som trez

More precisely in IPA:

/nu sɔm tʁɛz/

A few helpful points:

• nous sounds like noo
• sommes sounds like som
• treize sounds roughly like trez
• the final s in nous is not pronounced here
• there is no special liaison in this sentence

Yes. A few common ways:

• Nous sommes treize ? = We are thirteen? / Are there thirteen of us?
  (spoken, with rising intonation)

• Est-ce que nous sommes treize ? = standard spoken/written question

• Sommes-nous treize ? = more formal inversion

All three are correct.

Yes. It is a complete sentence.

French does not need to add anything else here, because the idea we are thirteen people is already complete and clear.

In context, it could answer a question like:

• Combien êtes-vous ? = How many are you?
• Nous sommes treize. = There are thirteen of us.

It is commonly used when talking about the size of a group, for example:

• a family
• a class trip
• a team
• guests at dinner
• people in a meeting

For example:

• Pour le dîner, nous sommes treize. = There are thirteen of us for dinner.

So the sentence is often used when counting how many people are included in a group.