Pronunciation of "~s" or "~es" (plural form)

a word ending with plosive consonant (p, t, k, f, th(θ)) (voiceless)  + s or es  ==> [s]
a word ending with "s" or "y" + s or es  ==> [iz]
the rest (voiced and vowel) + s or es  ==> [z]

exception: a word ending with "th"
mouths [z]
months [s]
clothes [z]