Rules for plurals in English

For regular nouns, add “s” to the

end
Cat = cats
Dog = dogs

If the singular noun ends in “y” and the letter before it is a consonant, drop it and add “ies”

Baby = babies
Ruby = rubies

If the singular noun ends in ‑s, -ss, -sh, -ch, -x, or -z, add ‑es to the end to make it plural.

Bus = buses
Lunch = lunches

If the singular noun ends in “fe” or “f” drop it and add “ves” (there’s exceptions to this rule)

Knife = knives
Leaf = leaves

If the singular noun ends in -y and the letter before the -y is a vowel, simply add an -s to make it plural

Ray = rays
Boy = boys

If the singular noun ends in ‑o, add ‑es to make it plural (there are exceptions to this one as well)

Potato = potatoes
Video = videos

If the singular noun ends in ‑us, the plural ending is frequently ‑i.

Cactus = cacti
Octopus = octopi

If the singular noun ends in ‑is, the plural ending is ‑es.

analysis – analyses
ellipsis – ellipses

If the singular noun ends in ‑on, the plural ending is ‑a.

phenomenon – phenomena
criterion – criteria

Some nouns don’t change at all when they’re pluralized.

sheep – sheep
series – series
species – species
deer –deer

As with almost every grammar rule in English, there are exceptions