My kitchen needed a new rug by the sink. We have cork floors, and for some reason the rubber backed rug we had was reacting with the finish on the floor and causing damage. So after resealing it, we needed something softer that wouldn't cause the same damage. I was really happy with how my first t-shirt yarn rug turned out, so it wasn't a hard decision to decide to make another. Only this one would be much smaller, and faster to knit up! A bonus is that it's nice and soft under our feet too.
I still had some leftover t-shirt yarn from the first rug, so I started off with that. Plus I had a bag full of discarded t-shirts ready to use. After choosing all blues/greens/greys/black ones that I had, I still had to buy a few more t-shirts to use. Luckily, my local thrift shop had a 50% off sale, so I bought 6 t-shirts for under $5 total (and didn't even use them all)!
I again used my biggest Knit Picks needles, with t-shirts cut about 4 cm (1-1/2") wide, and a plain garter stitch. I'm estimating that if only new large t-shirts were used, it would take about 10 or so. Finished size is 84 x 56 cm (33 x 22").