Best free personal item size for US airlines
The under-seat personal item that’s free on every US airline — including Spirit and Frontier.
Fits the personal item allowance on all 4 reviewed airlines in this group. The tightest is Allegiant Air.
How to use this recommendation
A US personal item must fit beneath the seat and is often the only free bag on value fares. This comparison concentrates on reviewed carriers where the under-seat item matters most and calculates a single conservative box for switching between them.
The trade-off
Aircraft fittings and seat supports can reduce usable floor space even when a bag meets the published maximum. A rigid item at the exact calculated size therefore carries more practical risk than a soft bag with a small margin on every side.
How we calculated it
We intersect the published included personal-item dimensions of the relevant reviewed airlines. The result covers the stated airline boxes, but it cannot guarantee a specific seat layout or override instructions from the operating carrier at the airport.
personal item limit per airline (4)
| Airline | Limit | Weight |
|---|---|---|
| Allegiant Air | 41 × 38 × 18 cm | — |
| Spirit Airlines | 45 × 35 × 20 cm | — |
| Sun Country | 43 × 33 × 23 cm | — |
| Frontier Airlines | 46 × 36 × 20 cm | 16 kg |
FAQ
What is the best personal item size for this group?+
A bag no larger than 41 × 33 × 18 cm (16.1 × 13 × 7.1 in), up to 16 kg fits the personal item allowance on all 4 airlines in this group — the limit is set by Allegiant Air.
Why not just buy the biggest bag?+
Because the strictest airline in the group wins. A bag that fits Allegiant Air fits everyone here; a larger one would be rejected or charged there. Buy for the tightest limit and you’re safe on all.
Should I leave a safety margin?+
Yes — measure with wheels and handles, and pick a bag a touch under the limit. A packed bag bulges, and low-cost airlines measure strictly at the gate.