Several regular countable nouns ending in f have special plurals: they change the f to v and then add -es:
calf / calves elf / elves half / halves knife / knives leaf / leaves life / lives loaf / loaves scarf / scarves self / selves sheaf / sheaves shelf / shel ves thief / thieves wolf / wolves
Several regular countable nouns ending in f make their plurals with either -ves or -s:
dwarf / dwarves (dwarfs) hoof / hooves (hoofs) staff / staves (staffs) wharf / wharves (wharfs)
Many regular countable nouns ending in f make their plurals by adding -s:
belief / beliefs bluff / bluffs brief / briefs chief / chiefs cliff / cliffs cuff / cuffs gaff / gaffs muff / muffs puff / puffs roof / roofs whiff / whiffs