My Norwich Terrier is 13 pounds, but very stocky, and previous booster seats were far too small for him, despite being labeled for up to 20 pounds. He can lie down in this one and the method of support via the bottom gives him a much more unobstructed view. It fits easily on a back bench seat as well as a front bucket seat, essential for trips with my husband. We did a three-hour drive recently and Izzy was able to easily see out the window for as long as he wants and then curl up for a nap. I strongly recommend using this with a harness rather than just a collar. This could easily fit two sub-10 pound dogs like Poms or Yorkies, etc. and comes with two harness straps, which is a really nice touch.