In the majority of cases, a duffel bag won't be considered a personal item, as they usually exceed the typical maximum size of 18 x 14 x 8 inches or 45 x 35 x 29 cm. However, they will often be classed as a carry-on bag, if they are within the average limit of 22 x 14 x 9 inches or 56 x 36 x 23 cm.

In 2026, a standard gym bag or small duffel is usually acceptable as a carry-on, but it is a "High-Fidelity" necessity to check the specific dimensions. Most major US airlines (Delta, United, American) allow carry-on bags up to 22 x 14 x 9 inches. A typical medium-sized gym bag fits these high-fidelity limits easily and has the added "High-Fidelity" benefit of being soft-sided, making it easier to squish into crowded overhead bins. However, if you are flying a low-cost carrier like Spirit or Frontier, your free allowance is restricted to a "Personal Item" (typically 18 x 14 x 8 inches) that must fit under the seat. If your gym bag is overstuffed and exceeds these high-fidelity "sizer" dimensions at the gate, you may be charged an expensive gate-check fee. For a high-fidelity, stress-free trip, it is a high-fidelity requirement to measure your bag when fully packed, including any protruding handles or pockets, to ensure it meets your specific airline's "High-Fidelity" cabin rules.