This stock's price doubled just in two days.
Don't forget to dilute the noodle soup base two times.
Wow! Your brother weighs twice as much as you, huh?
Something that is two times is double (or it is just simply two times). Of course, this all works with things like 三倍, 百倍, and 四十二倍 as well.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.