Personal item: (e.g., purse, small backpack, etc.): Dimensions must not exceed 18 x 14 x 8 inches (45 x 35 x 20 cm) including handles and wheels. Carry-on bag: Maximum of 22 x 18 x10 inches (56 x 46 x 25 cm) including handles and wheels.

For a duffle bag to count as a "carry-on" on Spirit Airlines, it must not exceed 22 x 18 x 10 inches (56 x 46 x 25 cm), including all handles and wheels. If you are hoping to bring a duffle bag as your "personal item" for free, it must be significantly smaller, measuring no more than 18 x 14 x 8 inches (45 x 35 x 20 cm), and it must be able to fit entirely under the seat in front of you. Spirit is notoriously strict about these dimensions; if your duffle bag is "overstuffed" and doesn't fit into the metal sizer at the gate, you could be charged an at-gate fee that often exceeds $100. Because duffle bags are soft-sided, they are often easier to squeeze into tight spaces, but they can also easily bulge beyond the permitted limits if not packed carefully. It is also worth noting that Spirit takes the weight of carry-on bags into account; typically, any bag over 40 lbs may be flagged. To save money, always pay for your carry-on bag at the time of booking, as the price increases significantly at check-in and reaches its peak at the boarding gate.