How it works
FitsOnBoard answers one question well: will this bag fit that airline?Here is exactly how we work it out, where our numbers come from, and where the limits of our data lie. No black box.
1. The sizer-box model
Airlines enforce cabin-bag limits with a rigid sizer box at the gate. A bag fits if — and only if — it slides into that box in some orientation. So we sort your bag’s three sides from largest to smallest, sort the airline’s limit the same way, and compare like with like. Turning your bag on its side never changes the verdict, exactly like the real box.
| Sorted side | Longest | Middle | Shortest |
|---|---|---|---|
| Airline limit | 55 | 40 | 20 |
| Your bag | 53 | 38 | 19 |
| Margin | +2 | +2 | +1 |
The tightest side has 1 cm to spare, which clears our 0.5 cm safety margin — so this bag is aFits.
2. The three verdicts
A yes/no answer hides the risk of a borderline bag. We give three, based on the smallest margin across all three sides:
Every side has at least 0.5 cm to spare. You can pack it and go.
It fits on paper, but at least one side is within 0.5 cm of the limit. A full or slightly bulging bag may be refused at the gate.
At least one side is over the limit. It won’t go in the sizer as cabin baggage.
Weight is checked the same way when an airline enforces a limit: over it is a fail, within 0.5 kg is tight.
3. How to measure your bag
- ▸ Measure the widest points, including wheels, handles and pockets — that’s what the sizer catches.
- ▸ Measure the bag packed, not empty; soft bags grow.
- ▸ Enter centimetres or inches — we convert with 1 in = 2.54 cm and show both.
4. Where our data comes from
The checker contains 151 airline records. Our 52 detailed airline guides show a “last verified” date and link to the airline’sofficial baggage policy. All 151 current database records carry aFits verifiedVerified status, but a standalone guide is published only after an additional manual editorial review.
We cross-check each airline’s limits against current sources on the shown date, reading the official page directly where the site allows it. “Verified” meanswe checked it recently and it matched — not that rules can never change. They do (Ryanair enlarged its free bag in 2025), so always confirm with the airline before you fly.
Bag dimensions come from manufacturers and are stored as externalmeasurements. Because makers sometimes quote sizes without wheels, we flag any bag within 0.5 cm of a limit as tight rather than promising a fit.
5. Recent review history
Rechecked the 25 published airline guides against first-party sources and added airline-specific fare explanations, warnings and worked examples. Corrections included the current Ryanair personal-item size, Lufthansa’s personal-item depth, JetBlue’s all-fare carry-on entitlement and the current Emirates cabin-bag depth.
Limited standalone airline, size and shared-size guides to manually curated allowlists. The full airline database remains available in the checkers, while incomplete editorial pages and the preliminary product catalogue are withheld from publication.
Published the sourcing, correction, privacy and commercial-independence standards and introduced a visible editorial credit across data-led pages.
6. Limits of the data
- ▸ Some airlines (e.g. Singapore Airlines) use a total-of-three-sides rule instead of a box; we show a representative box and note it.
- ▸ Fares differ: a limit free on a standard economy fare may be paid on a “basic/light” fare. We label free vs. paid and note the exceptions.
- ▸ Gate agents have discretion. A tight bag can pass on a quiet flight and be refused on a full one.
7. Affiliate disclosure
Product selection, fit calculations and commercial links are separate. Affiliate status, partner and commission are not inputs to the fit engine or the product-sorting functions. When a commercial link is active, it is marked “Ad” before you open it. Read our Affiliate disclosure and how we choose products.
Spotted an out-of-date limit?
Rules change and we would rather fix a number than mislead you. Tell us the airline and the correct dimensions and we’ll re-verify.
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