Say “IZ when the word ends in s, z, sh, zh, ch, or j sound.
Say “Z when the word ends in a vowel or other voiced sound like the m, n, ng, l, b, d, g, v, voiced th, or r sound.
Say “S when the word ends in a voiceless sound like a p, t, k, f, or voiceless th sound.
Here is the rule to help you:
When the letter 's' is after a vowel, another 's', or a voiced consonant, it is pronounced as a /z/ sound. e.g., logs, tubes, beds, moves, clothes, was, becomes, he's, passes. e.g., passes, beaches, washes, packages, noses.