Consult a dictionary. If you are unsure of how to translate a singular noun to a plural noun, then you can look up the singular form of the word in the dictionary.
Determine whether the word is a count noun or a noncount noun. A count noun has different forms based on whether it is referring to one object or more than one object. A noncount noun uses the same form for both types of objects. An example of a count noun is pen. There can be one pen or two pens. An example of a noncount noun is weather.
Add "s" to the end of the noun. If the noun is a count noun and it does not end in the letter "s," then you can add the "s" to the end of it. For example, if the singular noun is orange, then the plural noun is oranges.
Add "es" to the end of the noun. If the noun is a count noun and it ends in the letter "s," "x," "ch," or "ss," then add "es" at the end. For example, if the singular noun is bus, then the plural form is buses. If the singular is box, then the plural is boxes. If the singular is sandwich, then the plural is sandwiches. If the singular is class, then the plural is classes. This rule also applies to surnames that end in "s." The plural of Jones is Joneses.
Change the "us" ending of the word to an "i" if it has a Latin origin. For example, the plural form of nucleus is nuclei.
Change the "on" ending to an "a" if the word is of Latin origin. For example, the plural form of the word criterion is criteria.
Memorize some of the basic irregular plural forms. Some irregular plural nouns are used frequently. For example, people is the plural form for person. Men is the plural form for man. Teeth is the plural form for tooth.
Memorize some of the basic nouns that have the same singular and plural form. Examples of such words are deer and moose.