Open up the package and measure 8 inches of the elastic with a measuring tape. You can see in the photo that I didn’t pull it tight. It’s more of an eyeball measurement. You could make it longer if you want the tails to stick out a little longer too. Cut it with some sharp scissors. I prefer to use sewing scissors.
Take the edges and tie them in a double knot. Yes, it is that easy! I left about an inch at the end of each tail but if you want them a little longer, cut the length of the elastic 9 inches or so. If each one is 9″ you will get 3 hair ties out of these packages.
After the elastic is tied with a double knot, take a gas lighter and just barely burn the edges. This will prevent the edges from fraying.