In the English language, there are several grammar rules to follow if you want to use proper spelling and language skills. In general, there are very basic rules involving how to change a singular word to its plural equivalent. However, as with all areas of grammar, there are exceptions to this rule that complicate the language. It is always best to check a reference for accuracy any time you aren't certain about the plural form of a word. The basic rules apply to most words, though.
Add an "s" or "es" to the end of the word for most words in the English language. For any word that ends in a sibilant sound, such as s or z, use "es" to pluralize the word. In other cases use "s." For example: dog becomes dogs, boss becomes bosses.
Change the y to an i and add "es" to the end for words ending with a y that is not preceded by a vowel. For instance, pony becomes ponies.
Change the ending to "ves" for words ending in f. For instance, elf becomes elves and hoof becomes hooves.
Replace the vowels in certain words to make them plural. For example, woman becomes women and foot becomes feet.
Keep some words in their singular form to make them plural. For instance, the plural of sheep is sheep; the plural of offspring is also offspring.
Tip
These are not all of the exceptions to the rule, so for some words you may need to consult a dictionary.