Any cotton jersey knit can be turned into a woven, knitting or crochet project. You can use old T-shirts, odd socks, or any other garment made from stretchy fabrics.
One large men’s T-shirt cut to 1″2.5 cm will yield around 50 feet/15 meter of yarn, roughly equivalent to a skein of store-bought T-shirt yarn.
To maximize the amount of the yarn you can cut the t-shirt sleeves spirally and connect them to your skein*. Smaller pieces can be cut to stripes and connected to the yarn as well, but they can be saved for other smaller projects like scrunchies and small accessories.
Take your time! When first starting out it is better not to rush. Paying close attention to the cuts you are making will lead to better results. With time and practice you will be able to make better quality skeins in a shorter amount of time.
*T-Shirt or other jersey knit garment