How long is the main quest? [duplicate]

The game technically never ends because they continue to randomize quests after you have completed all of the handcrafted quests.

The main quest itself is supposed to take around 30 hours for an average game.

There are three acts with 6-7 quests in each act.

You can find all kinds of info on quests on the Skyrim Wiki. The Unofficial Elder Scrolls Pages are also a good resource.

The amount of time it takes is completely up to you.

The main quest is odd, because you'll probably end up doing a few sidequests without realising it. But the story line quest took me three days and I played around 3-4 hours each. So around 9 hours, and I was also a level 12 when I finished, so if you're higher it could be shorter still