In general terms there are 10 monophthong vowels plus 11 compound (dipthong) vowels.

Monophthongs: A monophthong is a single, pure vowel sound, represented by the 10 basic vowels in Hangul. Monophthongs maintain a single, steady sound. More complex Korean vowels are formed by combining these basic monophthongs.

Vowel (monophthong)	Romanisation	Pronunciation
	a
	ya
	eo
	yeo
	o
	yo
	U
	yu
	eu
	i

Diphthongs (or compound vowels): Diphthongs are combination of two vowel sounds. This is just a fancy way of saying that there are two vowels in one.