Well, it kind of depends. At lower levels, it used to just be 2-3 rounds and the battle would be over. Now that we're levels 10-12, and without significant magical help, there are a lot more hit points to hack away by both sides. In my last major battle, it probably took my paladin (with his trusty cohort at his side) 3 minutes to hack down 5 blood thirsty vampires. It was an extremely close battle, with lots of healing and lots of hacking. My saves are so high (hehe, I love paladins) that their death magic wouldn't hurt me, so it was basically a slug fest.
In large scale battles, 10, 20, 30 foes on the board at once, it's not unusual to see 10-20 round combats. With fewer foes, it's easier to concentrate damage, so those combats usually only last 4-5.
In large scale battles, 10, 20, 30 foes on the board at once, it's not unusual to see 10-20 round combats. With fewer foes, it's easier to concentrate damage, so those combats usually only last 4-5.