Yes, Frontier Airlines has some of the most restrictive baggage size limits in the industry, and their carry-on requirements are slightly smaller than most major U.S. "legacy" carriers. While airlines like Delta or American allow carry-on bags up to 22 x 14 x 9 inches, Frontier's limit for a paid carry-on is 24 x 16 x 10 inches (which is actually slightly wider but more strictly enforced via metal "sizers" at the gate). The real difference is the free personal item, which Frontier limits to 18 x 14 x 8 inches. Unlike many other airlines that rarely measure bags, Frontier gate agents are famously rigorous about checking that bags fit completely within the dimensions. If your bag exceeds these limits even by an inch due to wheels or handles, you will be forced to pay a "gate-check fee," which can be significantly more expensive (often $99 or more) than prepaying for a bag during the initial booking process.