@makayla20 Usually a good length for strings is the full length of your arm to your opposite shoulder, about 100 cm or 40 inches. Double that if you plan to fold them in half to make a loop.
For any pattern in general, take a look at the knot structure as well, because some patterns have strings that are barely used for knots, so those strings could be shorter. Sometimes certain strings may need to be longer if they use knots for most of its entire path, or if you plan to have long ties on both ends.
It’s also a good idea to keep a notebook of how long you actually cut your strings for each pattern and how much you have leftover, or if you run out. Then you can get a better idea what to do for future patterns 😊