If you see an s or se at the end of the word, it is usually pronounce /z/. Check the dictionary to be sure.
Spelled letters -ss, say /s/
examples: glass, grass, less, guess
Spelled letters -ce, say /s/
examples: ice, place, space, face
Spelled letter -s, Usually /z/
examples: was, is, goes, his, as, eyes (say "waz, iz, goez, hiz, az, eyez")
Spelled letter -s, (sometimes s)
examples: yes, us
Spelled letters -se, Usually /z/
examples: those, use, these, please (say "thoz, uz, thez, pleaaz")
Spelled letters -se, (sometimes s)
examples: house, goose, lease