The need to understand how a Frontier personal item size would be so different from that of a carry-on will save some extra fees. Frontier personal item size is 14" x 18" x 8" in dimensions, including handles and wheels, free to carry, with the inclusion of small backpacks, purses, and laptop bags. However, a carry-on has to be less than 24" x 16" x 10" and is subject to extra charges... https://www.airlinereservationwindow.com/frontier-airlines-personal-item-size-limit/