The pronunciation of -s/-es at the end of plural nouns, verbs in third person and as a part of the possessive case can be pronounced in three different ways: /ɪz/, /s/ or /z/.
1. The /ɪz/ or /əz/ sound
If the last consonant sound of the word is the list below, the final -s/-es is pronounced as /ɪz/. This /ɪz/ sound is pronounced like an extra syllable.
S: pauses, nurses X: fixes, boxes
Z: amazes, freezes CE: races,dances
SS: kisses, misses CH: churches, teaches
SH: pushes, crashes GE: garages, changes
Note: after verbs ending in -sh, -ch, -ss and -x, we add the -s/-es to the end of the verb in third person and the pronunciation is /iz/ as an extra syllable.
2. The /z/ sound
If the last letter of the words ends in a voiced consonant (or sound), then the S is pronounced like a /z/.
B: crabs, rubs D: cards, words
G: rugs, bags L: calls, hills
M: plums, dreams N: fans, drains
NG: kings, belongs R: wears, cures
V: gloves, wives Y: plays, boys
THE: clothes, bathes VOWEL SOUNDS: sees, fleas
3. The /s/ sound
If the last consonant of the word is voiceless, then the -s/-es is pronounced as /s/. Be careful not to create an extra syllable.
P: cups, stops T: hats, students
K: cooks, books TH: tablecloths, months (voiceless th)
F: cliffs, beliefs, laughs, graphs
(the -gh and -ph here are pronounced like a F)