The simple answer is one to four minutes.
Always lead with your best footage. Pretend your reel is a guest at a party. A good guest is engaging, entertaining, and doesn’t overstay their welcome. That’s what you want your reel to be.
Casting Directors (one minute):
Like in an audition, they know if they’re interested in you within the first 30 seconds.
Agents (No more than three to four minutes).
They can see immediately what you have to offer. Generally, they are looking to see how many different ways they can sell you.
If you want a reel that is four to five minutes long, it should be for a specific request. If you’re going over four minutes, you’re getting into “short Film” territory, and that might not helpful to anyone.