Yes, Frontier Airlines is known for being strict about carry-on bag sizes, especially for their "personal item" allowance. They will check the size of personal items before boarding and may charge a fee if it doesn't fit within the allowed dimensions.

Frontier Airlines enforces its carry-on baggage policy quite strictly to ensure cabin safety and comfort, so passengers should plan accordingly. By default, every ticketed traveler is allowed one personal item—such as a small backpack, purse, or laptop bag—that must fit under the seat in front of you; any additional carry-on larger than the dimensions of 18″×14″×8″ is considered a standard carry-on bag and requires purchasing the “Carry-On” fee, which can cost significantly more if paid at the gate. If you arrive at the boarding gate with an unpaid carry-on, Frontier will automatically move your bag to the cargo hold and charge you the gate fee, which can exceed \$60–\$70 depending on the route and demand. To avoid these last-minute charges, it’s wise to prepay for a carry-on during online check-in or via the Frontier app, and if you need assistance or clarification about the size limits or applicable fees, you can call Frontier customer service at +1-866-551-1186. Gate agents routinely measure baggage, and any bag that exceeds the limit of 10 kg (22 lb) or the approved dimensions of 24″ × 16″ × 10″ will be flagged. Frontier’s policy on personal item vs. carry-on is non-negotiable: even a slightly oversized “personal item” may be reclassified as a standard carry-on, triggering extra fees. Families traveling with infants should note that while the infant’s “diaper bag” may be carried free of charge, all other carry-ons must comply with standard rules. Frequent travelers often cite Frontier’s strict approach as one of the most rigorous among U.S. airlines, and although occasional leniency can occur if the flight isn’t full, it is not something to count on. To guarantee compliance, travelers should weigh and measure their bags at home, pack minimally, and understand that Frontier prioritizes low fares by enforcing strict carry-on regulations—so checking in ahead of time, purchasing any required carry-on allowance in advance, and verifying baggage rules via Frontier’s official website or by calling +1-866-551-1186 can prevent unexpected expenses and ensure a smoother boarding experience.