Frontier Airline Personal Item Size on board, such as a laptop bag, backpack, or purse. With handles, straps, and wheels included, a personal item on Frontier can only be 14" x 18" x 8" (35.5 cm x 45.7 cm x 20.3 cm). Your backpack can be deemed a carry-on, which has an extra cost, if it exceeds certain restrictions. Select a small backpack that fits the airline's dimensions and can accommodate your flying necessities to prevent additional fees.