The wasted-allowance gap: how much free cabin space you leave behind with only a personal item

Short answer: a personal item alone uses a fraction of your free cabin allowance. Pair it with the carry-on every airline includes and the free total runs from about 69 L (European legacy) to 79 L (US carriers). Travelling with only a 6 L personal item leaves 60–73 L of free space on the table — space you have already paid for in your fare.

Two free bags, not one

Almost every fare includes two free cabin items: a carry-on and a personal item. The personal item gets the attention because it is the one that gets measured at the gate, but the carry-on is the larger of the two and it is also free.

The gap is the point

A 25 × 17 × 14 cm bag is 5.95 L. On a European legacy fare, showing up with only that bag means you are using 6 L of a 68 L free allowance — you have left roughly 63 L of space you already paid for. That is not a violation; it is just unused. The personal item is the bag you keep with you; the carry-on is the bag you stow. Both are free, and the depth limit applies to the one you keep.

Where the low-cost model differs

Low-cost carriers shrink or charge for the carry-on. Ryanair's free allowance is only the 40 × 30 × 20 cm under-seat item; the bigger cabin bag is an add-on. So on those fares the "wasted allowance" is smaller because there was less free to begin with — which is exactly why a free personal item that fits every sizer is worth more on a budget ticket.

Should you buy the Jelkin 25 for this?

Travelling with only a 6 L personal item leaves 60–73 L of allowance you already paid for. So this bag is not a substitute for a carry-on — it is the other half of a pair. Buy it if you already have a stowed bag and want the under-seat half to be guaranteed free; read the volume page first if you want one bag to do everything.

How to check this yourself before you fly

1. Check what your fare actually includes. Legacy fares bundle a carry-on and a personal item; low-cost fares usually keep only the personal item free.
2. Let the carry-on do the volume work and the personal item do the access work — things you need mid-flight.
3. Measure the personal item's depth against 15 cm, because that is the number the gate checks on the item you keep with you.
4. Do not treat a 4.2 L bag as your only luggage for more than a day trip. That is how people end up buying a second bag at the airport.

Keep reading:

• airline personal item size checker — all 19 carriers side by side
• one-centimetre depth cliff — why 15 cm decides six airlines
• the 25 cm bag that fits every sizer — length-vs-depth end to end
• why external dimensions lie about capacity — how we measure bags
• Jelkin 25 — the 25 × 17 × 14 cm bag measured on this page