How do you say his in French?

In French there is no distinction between "his", "her(s)", or "its". No matter who or what the possesser is, you use son (m), sa (f), or ses (pl) depending on the noun being modified. For example:

son bureau (his/her/its desk)

sa taille (his/her/its size)

ses animaux (his/her/its animals)

Exception: Never use "sa" in front of a word that starts with a vowel or non-aspirate h. Instead use "son" and pronounce it with the liaison. For example: "son image", "sa hauteur", "son immense hauteur").

Remember: choose "son" or "sa" according to the gender of the modified noun, not the gender of the person as in English.

To translate a phrase like, "that car is his", use the preposition à before a noun a pronoun. For example, "that car is his" could be translated as "cette voiture est à lui".