The answer is: it depends.
Depends on size of the rubber band, condition, and the rubber qualities.
Which can vary from batch to batch. The rubber is not consistent in quality
even with the same size and manufacturer.
So what to do? Again, I recommend Don Ross' book on rubber powered models. There is a chart that gives an idea of how much to wind a rubber motor. But, it's not guaranteed.
You can always buy some rubber and test how many winds until it breaks.
Then when you put a rubber motor in your model; go about 90% of turns it took to break it.
Pre-stretching or "breaking in" the rubber has a great affect on how much you can wind it. Cleaning and lubing also has a big affect.
Just as a rough idea..... for 3/32" width rubber you can wind 100 turns for every inch of relaxed length.( the rubber must be cleaned, lubed, and pre-broken in)
For example: If your rubber loop is 15 inches long, you can stretch-wind 1500 turns, with FAI tan II rubber. (100x15=1500)This isnot the rubber supplied in the kits.
The rubber supplied in most of the Guillow kits can only be wound 75 to 125 turns. Thats all. After a couple of flights, throw the rubber away. It will break easily.