First, lay your t-shirt flat. Cut off the hemmed end and discard.
Just a warning...this does make a bit of a mess on your cutting mat.
Working from the bottom of the shirt, cut in 1/2" strips, leaving the side seams in tact. This will form loops.
Using a P hook, chain stitch to desired width. I started with 50 stitches and my rug is approximately 30" wide. Chain one more. (to use for turning)
(Ok, I am going to change colors here, because this rug is already in progress.)
Single crochet in each space.
Flip over the rug and begin working in the first space with a single crochet.
Keep working back and forth until the rug reaches the desired length.
Knot and weave in the end.
If you make a rug using this tutorial, I'd love to see it.