The double bass is the largest member of the violin family (string family). It stands at around 180cm tall, though some players prefer shorter versions. For this reason, the player either stands or sits on a high stool. It is also not uncommon to have a 3/4 double bass. Some people question the instrument’s origins, often due to the unique tuning used for the double bass: it is the only instrument within the family that is tuned in perfect fourths. As such, the tuning notes of the strings are E1-A1-D2-G2: the complete opposite of the violin, wherein E is the highest. The open strings are the same as in the electric bass.

Source: Violinspiration