Conditions
Check in luggage size: the number the airline publishes, and the three you measure
Check in luggage size is set by your carrier, not by screening. How linear inches work, what the published weight caps leave you, and how to measure a case over its wheels.
Check in luggage size is one of the few travel numbers that is genuinely easy to get right, and it still goes wrong constantly. The reason is that people look it up in the wrong place: they ask what security allows, when screening sets no size at all, or they trust the number printed on the case rather than the one a tape measure gives across its wheels.
This guide separates the figure your carrier publishes from the figures you have to produce yourself. It uses one airline's published allowance as a worked example throughout, so the arithmetic is concrete, and it is clearly labelled as that carrier's figure rather than a rule that applies everywhere. No price is quoted here, because fees change and the measurement logic does not.
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Screening does not set the figure, so stop looking there
The Transportation Security Administration answers this directly in its own frequently asked questions. Its wording is that the size dimensions of carry-on baggage allowed in the cabin of the aircraft vary by airline, and it tells travellers to contact their airline about what will fit in the overhead bin or under the seat in front of them. Screening has rules about what may be inside a bag. It has none about how large the bag is.
That single fact reorganises the whole problem. The figure you design around lives on a baggage page belonging to the carrier whose aircraft you are actually boarding, and it can differ between that carrier's own cabins and even between its own aircraft types. Delta publishes, for instance, that on its Delta Connection flights operated with 50 seats or fewer, passengers may only carry personal items into the cabin, because the overhead space is not there.
So the practical sequence is: book first, then read that carrier's published baggage page, then measure. Doing it in the other order means you measure against a number you half remember from a different airline, which is how a case that has flown happily for years suddenly fails at a gate.
Linear inches is one number doing the work of three
Most carriers express a hold-bag limit as a single combined figure rather than as three separate sides. Delta's published hold allowance is a maximum of 62 inches (157 cm) when length, width and height are added together. A cabin limit is often written the same way: that carrier states a combined maximum of 45 linear inches (114 cm), and additionally caps each individual side at 22 x 14 x 9 in (56 cm x 35 cm x 23 cm).
A combined figure is more forgiving than three separate caps, because it lets you trade one dimension against another, but only where no individual cap also applies. Under a pure 62 inch combined limit, a tall narrow case and a short wide case can both qualify. Under a cabin rule that carries both a combined figure and per-side maximums, the per-side maximum is usually the one that bites first, so check that your shortlist clears both.
The arithmetic is worth doing once by hand, because it shows how little room a combined limit really leaves. Add your three outside dimensions, including wheels and handle housing, and compare the sum against the published figure. The table below works that sum for three example cases against the 62 inch combined limit so you can see what passes and by how much.
| Example case, outside H x W x D | Sum of the three sides | Against a 62 in combined limit | Margin left |
|---|---|---|---|
| 29 x 20 x 12 in | 61 in | passes | 1 in |
| 30 x 21 x 13 in | 64 in | over | 2 in over |
| 28 x 19 x 11 in | 58 in | passes | 4 in |
The 62 inches (157 cm) combined figure is Delta's published hold-bag maximum. Other carriers publish their own. The sums are plain addition, and they assume you have measured over the wheels and the retracted handle.
The weight cap is a second, independent gate
A bag that clears the dimensions can still be turned back on mass, because size and weight are separate published limits. Delta states that standard hold bags must be under 50 lbs (23 kg) per piece, and that Delta One and Delta First allow up to 70 lbs (31.8 kg) per piece. A larger cabin on the same aircraft can therefore carry a heavier allowance for the same physical bag.
Because every weight cap is a gross figure, the empty case is spending part of it before anything goes in. That is the number shop displays rarely show and the one that decides whether you repack on the floor at the desk. Under a 50 lbs cap, a hold case whose own shell weighs 11 lbs leaves 39 lbs of contents; one that weighs 8 lbs leaves 42 lbs, which is roughly 8 percent more packed weight for the same allowance and the same trip.
None of this makes a heavier shell wrong. A rigid case protects things that crush, closes reliably when overfull, and keeps weather out. The honest framing is that you are spending part of a fixed allowance on protection, and it is better to know how much of it you are spending than to discover it on a scale.
| Empty case weight | Contents under a 50 lbs cap | Contents under a 70 lbs cap |
|---|---|---|
| 8 lbs | 42 lbs | 62 lbs |
| 11 lbs | 39 lbs | 59 lbs |
| 14 lbs | 36 lbs | 56 lbs |
The 50 lbs (23 kg) standard cap and the 70 lbs (31.8 kg) Delta One and Delta First cap are that carrier's published figures. Subtraction is ours. Empty weights are illustrative; weigh your own case.
Measure over the wheels, because that is what a sizer meets
Delta's carry-on page is explicit that its measurements include any handles or wheels. Treat that as the general method even where a carrier does not spell it out, because a sizer frame and a desk scale both meet the extreme point of the object rather than the shell the label described. A case advertised as 22 inches tall that reaches 23.5 inches across its spinner housings is, for this purpose, a 23.5 inch case.
The method takes about 2 minutes. Stand the case upright on a hard floor with the handle fully retracted and the packing straps done up. Measure height from the floor to the highest fixed point, which is usually the handle bar or the top edge, not the soft lid dome. Measure width across the widest point including any side feet, and depth from the back face across the front pocket when it is full rather than empty.
Write the three numbers on a luggage tag or inside the lid. You will need them again when you book a different carrier, and they are the only version of the case's dimensions that is actually true. If one figure sits within about 1 inch of a published cap, assume it will be challenged at some point and plan accordingly.
- Retract the handle fully and fasten every external strap before you start.
- Measure with the front pocket packed as you would actually pack it, not flat.
- Include wheel housings in height and side feet in width.
- Record all three figures plus the empty weight, and keep them with the case.
Some items choose their own bag, and that fixes part of the load
Two sets of rules will decide where part of your packing goes regardless of how the dimensions work out. The Federal Aviation Administration states that spare, uninstalled lithium ion and lithium metal batteries, including power banks and battery charging cases, must be carried in carry-on baggage only, and that when a cabin bag is checked at the gate or planeside, all spare batteries and power banks must be taken out and kept with the passenger in the cabin.
That agency also publishes the size limits behind the rule. Lithium metal, non-rechargeable, batteries are limited to 2 grams of lithium content per battery, and lithium ion, rechargeable, batteries to a rating of 100 watt hours per battery. With airline approval, a passenger may also carry up to 2 spare larger lithium ion batteries in the 101 to 160 watt hour band, and terminals must be protected against short circuit. It notes that individual carriers may set stricter limits on how many power banks you may bring.
Liquids work the other way round: they are a cabin restriction, and the hold is where volume is free. The screening agency's figure is travel-size containers of 3.4 ounces or 100 millilitres, with each passenger limited to one quart-size bag of liquids, gels and aerosols. So anything over that container size either travels in the hold or does not travel, and the cabin bag you buy has to hold that quart bag, a laptop and whatever you refuse to be separated from.
| Item | Published requirement | Effect on your packing |
|---|---|---|
| Spare power bank or loose lithium battery | Carry-on only; removed and kept with the passenger if the bag is gate-checked | Reserve cabin space; never bury it in the hold case |
| Lithium ion battery above 100 watt hours | Airline approval needed; up to 2 spares in the 101 to 160 watt hour band | Ask before travel day, not at the gate |
| Liquid in a container over 3.4 oz / 100 ml | Not permitted through screening in the cabin bag | Goes in the hold bag, which is where volume costs nothing |
Battery figures are the Federal Aviation Administration's packsafe guidance; the container figure is the screening agency's liquids rule. Carriers may be stricter.
Settling it before you buy, and before you leave
Put the decision in order and it stops being a guess. First, find the published combined figure and weight cap for the carrier and cabin you have booked. Second, measure any case you already own over its wheels and handle, and weigh it empty. Third, subtract the empty weight from the cap to see what you are really allowed to pack. Only then does the question of which case to buy have a usable answer.
If you fly several carriers a year, build to the meanest allowance you expect rather than the most generous, and accept the unused margin on the roomier airlines. A case sized for a 45 linear inch cabin rule fits everywhere that publishes more; a case sized for a generous rule fits nowhere that publishes less. That asymmetry is the whole argument for buying small.
Finally, treat every figure in this guide as a dated snapshot of a published document rather than a permanent fact. Allowances are commercial decisions and they are revised. The habit that protects you is re-reading the baggage page of the specific carrier each time you book, which takes about 3 minutes and removes the entire category of problem.
Before you buy
- Open the baggage page of the exact carrier and cabin you booked, and write down the combined dimension figure and the weight cap.
- Check whether the cabin rule carries per-side maximums as well as a combined figure.
- Measure your case upright, handle retracted, straps fastened, over wheels and side feet.
- Add the three sides and compare the sum against the published combined figure.
- Weigh the case empty, then subtract that from the weight cap to get your real packing allowance.
- Move spare batteries and power banks into the cabin bag before you leave home.
- Keep liquids over 3.4 oz / 100 ml in the hold bag, and keep one quart-size bag accessible in the cabin.
- Re-read the carrier's baggage page at every new booking, because the figures are revised.
Questions readers ask
- Does one national rule set check in luggage size in the United States?
- No. The screening agency states in its own frequently asked questions that cabin baggage size varies by airline and directs travellers to contact the carrier. Hold-bag dimensions are likewise published by each airline rather than by a federal body.
- What does a 62 inch limit actually mean?
- It means length plus width plus height added together must not exceed that figure. Delta publishes 62 inches (157 cm) as its hold-bag maximum. Because it is a combined figure, you can trade one dimension against another unless a separate per-side cap also applies.
- Do wheels and handles count towards the measurement?
- On the carry-on page used as an example here, yes: the carrier states the measurements include any handles or wheels. Measure to the extreme points of the packed case, because that is what a sizer frame and a desk will meet.
- Can I put a power bank in my hold bag to save cabin space?
- No. The Federal Aviation Administration states that spare lithium batteries and power banks must travel in carry-on baggage only, and that they must be removed and kept with the passenger if a cabin bag is checked at the gate or planeside.
- How much weight does the empty case itself use up?
- More than most people expect, because weight caps are gross figures. Under a published 50 lbs (23 kg) cap, an 8 lbs case leaves 42 lbs of contents and a 14 lbs case leaves 36 lbs, a difference of about 17 percent in what you can pack.
Sources
- Transportation Security Administration — Frequently asked questions (carry-on size varies by airline; liquids rule) — checked 2026-11-06
- Delta Air Lines — Baggage overview (checked bag 62 in / 157 cm combined; under 50 lbs / 23 kg; up to 70 lbs / 31.8 kg in Delta One and Delta First) — checked 2026-11-06
- Delta Air Lines — Carry-on baggage (45 linear inches / 114 cm; 22 x 14 x 9 in; measurements include handles and wheels) — checked 2026-11-06
- Federal Aviation Administration — PackSafe: lithium batteries (carry-on only for spares; 2 g lithium metal; 100 Wh lithium ion) — checked 2026-11-06
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