Minimum 30 secoinds, maximum 2 minutes, except for maybe having to setup equipment, and dissasemble free weight equipment, between exercises, then you have to allow for possibly over two minues.
In general I think most people like to go for 60-90 second breaks.
probably depends nore so on what you're training for
strength 3+ mins
hypertrophy 30 - 90secs
fat loss - 45secs
it all depends though
if doing low reps for sterength than abide by 3+min rest rule and but if doing say 10 x 3 for strength and mass than rest about 60 - 70secs which is probably better
Just in case you're wondering what Swanso means by hypertrophy (he uses fancy words a lot), he means training for muscle volume. If you wait more than about 1 minute between sets, you will continue to recruit the same muscle fibers, which is great if you want those to be strong, such as in power lifting. If you want to recruit as much muscle fiber as possible, creating a larger and fuller muscle, then you should wait 30-60 seconds between sets, and sometimes less. For example, when running the rack at the end of an exercise. In this case, you would wait almost no time in between sets, as you want to destroy the muscle by doing 10s of reps in a row by slightly dropping down in weight until you've done almost all of the weights on the rack, hence the name.