According to Catholic teaching; how long do we go to Hell for?

It is interesting that a much higher percentage of people believe in the existence of heaven than believe in the existence of hell. According to the Bible, though, hell is just as real as heaven. The Bible clearly and explicitly teaches that hell is a real place to which the wicked/unbelieving are sent after death. We have all sinned against God (Romans 3:23). The just punishment for that sin is death (Romans 6:23). Since all of our sin is ultimately against God (Psalm 51:4), and since God is an infinite and eternal Being, the punishment for sin, death, must also be infinite and eternal. Hell is this infinite and eternal death which we have earned because of our sin.

The punishment of the wicked dead in hell is described throughout Scripture as “eternal fire” (Matthew 25:41), “unquenchable fire” (Matthew 3:12), “shame and everlasting contempt” (Daniel 12:2), a place where “the fire is not quenched” (Mark 9:44-49), a place of “torment” and “fire” (Luke 16:23-24), “everlasting destruction” (2 Thessalonians 1:9), a place where “the smoke of torment rises forever and ever” (Revelation 14:10-11), and a “lake of burning sulfur” where the wicked are “tormented day and night forever and ever” (Revelation 20:10).

The punishment of the wicked in hell is as never ending as the bliss of the righteous in heaven. Jesus Himself indicates that punishment in hell is just as everlasting as life in heaven (Matthew 25:46). The wicked are forever subject to the fury and the wrath of God. Those in hell will acknowledge the perfect justice of God (Psalm 76:10). Those who are in hell will know that their punishment is just and that they alone are to blame (Deuteronomy 32:3-5). Yes, hell is real. Yes, hell is a place of torment and punishment that lasts forever and ever, with no end. Praise God that, through Jesus, we can escape this eternal fate (John 3:16, 18, 36).

More on Hell, from the Athanasian Creed:

"At [Christ's] coming all men shall rise again with their bodies; and shall give account of their own works. And they that have done good shall go into life everlasting and they that have done evil into everlasting fire."

This is to be believed by all Christians. At the end of the Creed, it says:

"This is the catholic faith, which except a man believe faithfully he cannot be saved."

More on Hell, from St. Robert Bellarmine, Doctor of the Church:

"Now if it were a matter of caution that, by the edict of a king, at a certain hour, no one should set foot outside the city gates, under penalty of death by hanging, who would be found to be so negligent and heedless of his own safety that, at the forbidden hour, and in the presence of many witnesses, he would venture to set his foot outside the gate? And if perchance for some reason he were to do this, would he not afterward be afraid, not only of the witnesses but also almost of the very gate itself -- as if it were somehow conscious that a crime had been committed? Now all Christians have been persuaded that the Almighty and most Excellent God has decreed by an irrevocable sentence that he who departs this life guilty of having [grievously] violated God's law is bound over as a convict to eternal chains and is tortured without end by unspeakable torments [if he does not sincerely repent of his sins before death]. Nevertheless, we see daily that many people, under no compulsion, unasked, and often even uninvited, offend God with their own initiative, free will and pleasure of mind. Indeed, they even seek occasions of sin, rejoicing when they find them and grieving when they do not. What shall we say is the cause of this?"*

*A Sermon on Hell delivered at Louvain University, Belgium, in approximately 1574 and being one of 5 sermons given by the Saint on "The Four Last Things" -- Death, Judgment, Heaven and Hell.