Theres a lot of variables.
For strength: 2-3 minutes
For size/fat loss: 30-60 seconds
For endurance: 30-90 seconds
These are really just arbitrary numbers because everyone is different, and you can make progressions based on shortening rest breaks.
Also, if your alternating between two exercise, your increasing the rest breaks.
Rest 60 sec.
Rest 60 seconds repeat
This will equate to about 150 seconds rest or more for each exercise, which is plenty for most goals
The main thing, is that like I stated above, these numbers are pretty arbitrary.
But you could make a general assumption that if your training for pure strength, take longer rest breaks, and if anything go too long, and if your training for hypertrophy, fat loss, or endurance, take shorter rest breaks, and use supersets if necessary to increase the time between sets.
Hope this helps.