This is the only place where the word firkin appears in the Bible. It was the main liquid measure of the Roman would in New Testament times. A firkin was equal to about nine gallons.
Jesus directed that these huge jars should be filled with water, then He turned the water into wine (John 2:7-9). According to the Gospel of John, this was the first of Jesus’ many miracles (John 2:11).
JOHN 2:6 – There were set there six waterpots of stone. . . containing two or three firkins apiece [each holding from twenty to thirsty gallons, NIV]