How to choose
Carry-on or checked: which suitcase to buy first
Cabin case or hold case, hard shell or soft side: the four numbers that decide which suitcase to buy first, and why tare weight beats the price tag.
Almost every suitcase regret is a measurement problem rather than a quality problem. The case was bought to a number somebody half remembered, it was measured without its wheels, and the first time it met a sizer frame at a gate it lost.
This guide works through the four numbers that settle the decision: the dimensions your carrier publishes, the empty weight of the case itself, the depth the wheels take away, and what has to travel in the cabin whatever else you do. Every price and dimension below is a worked example, clearly labelled as one, because no live price feed is connected to this site.
The limit belongs to the airline, not to security
The Transportation Security Administration publishes this in its own travel FAQ: the size dimensions of carry-on baggage allowed in the cabin vary by airline, and the agency directs travellers to the figure their carrier publishes. Screening sets no size at all. So the three numbers you design around sit on a baggage page belonging to the airline you actually fly, and the sizer frame at the gate is built to those numbers rather than to anything federal.
Measure a case the way a sizer does: lay it flat, and measure to the extreme points, which means over the wheel housings and over the retracted handle bar. A case sold as 22 inches tall that measures 23.5 inches over its spinner wheels is a 23.5 inch case, and the frame does not care what the label said.
External volume is the figure that tells you what the case can actually swallow, and it is a multiplication you can do in your head. The table below converts three example cabin specifications into cubic inches and litres so you can see how fast capacity falls when a carrier is 1 inch meaner in each direction.
| Example spec, H x W x D | External volume | Usable at 85% packing efficiency |
|---|---|---|
| 22 x 14 x 9 in | 2,772 cu in, about 45 litres | about 38 litres |
| 21 x 14 x 8 in | 2,352 cu in, about 39 litres | about 33 litres |
| 20 x 13 x 8 in | 2,080 cu in, about 34 litres | about 29 litres |
One cubic inch is 0.016387 litres. The 85% column allows for the shell, the lining and the fact that clothes do not fill corners. Dropping 1 inch in each direction costs about 13% of the volume between the first and second rows.
Tare weight is the part of the allowance you give away
Every weight cap is a gross figure, so the empty case eats the allowance before anything goes in it. This is the number that shop displays never show and the one that decides whether you repack at the desk.
On a 22 lb cabin cap, a 5.5 lb soft-side case leaves 16.5 lb of contents and a 7.5 lb hard-shell spinner leaves 14.5 lb. That is about 14% more packed weight for the lighter shell, for the same cap and the same trip. On a 50 lb checked cap the gap narrows in percentage terms, because the cap is bigger: 41.5 lb against 39.0 lb is about 6% more.
A hard shell is not wasted weight. It protects contents that crush, it closes reliably on an over-full load, and it keeps rain out. The honest trade is that you are spending part of your allowance on protection, and you should know how much of it you are spending before you choose.
| Case type | Example empty weight | Contents under a 22 lb cabin cap | Contents under a 50 lb checked cap |
|---|---|---|---|
| Soft-side cabin, 2 wheels | 5.5 lb | 16.5 lb | not applicable |
| Hard-shell cabin, 4 wheels | 7.5 lb | 14.5 lb | not applicable |
| Soft-side checked, 2 wheels | 8.5 lb | not applicable | 41.5 lb |
| Hard-shell checked, 4 wheels | 11.0 lb | not applicable | 39.0 lb |
Every cell is the cap minus the empty weight. The empty weights are example figures of the kind printed on a specification sheet; weigh the case you own rather than trusting ours.
Wheels and handles: the depth you lose and the parts that fail
Four-wheel spinner housings sit outside the shell, so they add to the measured height without adding anything you can pack. In the example specifications above, a spinner assembly that stands 1.5 inches proud turns a 22 inch allowance into about 20.5 inches of packable body, which is roughly 7% of the height gone before you open the lid.
Two inline wheels recess into the shell and roll better over kerbs and broken pavement, at the cost of carrying the case on an angle. Four wheels push rather than pull, which matters in an airport corridor and matters much less on a cobbled street. Neither is correct; they fail in different places.
Both fail at the same two components, and that is the useful part. Wheels wear flat and handle tubes bend, and on a case built with bolted wheel housings and a bolted handle both are replaceable. A wheel set at an example $18 and a handle assembly at an example $35 is a $53 repair that can double the life of a case, and the cost-per-use arithmetic in our budget guide shows exactly what that does to the per-trip figure.
- Turn the case over and look at the wheel housings: bolts and a visible axle mean a replaceable part, a moulded-in wheel means the case is finished when the wheel is
- Pull the handle to full extension and push sideways on it; more than about an inch of play at the top means the tubes are already loose
- Check whether the manufacturer lists wheels, handles and zip pulls as spare parts at all before you buy
- Measure the case over its wheels and handle with a tape, not over the shell, and write the number on a luggage tag
What has to travel in the cabin decides the cabin bag
Some items cannot be put in the hold, and that constrains the cabin case rather than the checked one. The Transportation Security Administration states that spare, uninstalled lithium ion and lithium metal batteries, including power banks and cell phone battery charging cases, must be carried in carry-on baggage only. Larger spares in the 101 to 160 Wh range are limited to two per passenger and need the airline to agree in advance.
The liquids rule constrains the same bag. Containers of liquids, aerosols, gels, creams and pastes are limited to 3.4 ounces, or 100 millilitres, each, and they travel in a single quart-sized bag; medications and infant or child nourishment are excepted from that limit. A quart bag has to come out of the case and onto the belt at most checkpoints, so it needs to live somewhere you can reach without unpacking.
Those two rules together describe the cabin bag you want: an outer pocket that opens without unzipping the main compartment, a sleeve that holds a laptop and a power bank where you can lift them out in one movement, and a shell that will lie flat and open on a bench. A beautiful case you have to kneel on the floor to open is a case you will stop using.
Choosing on your own trip pattern
Trips per year is the variable that decides the order of purchase, because it decides which case gets used. Somebody who flies twice a year for a fortnight each time needs the checked case first and can borrow a cabin bag. Somebody who flies eight times a year for two or three nights will use a cabin case on every one of those trips and a checked case on none of them.
Trip length sets the second number. A four-night trip fits a cabin case comfortably for most people; a seven-night trip fits it only if you will do laundry or wear the bulky items. Our packing guide does that arithmetic item by item, and the pack-weight calculator on this site will take your own list.
The sequence below is the one that wastes least money. It assumes you own nothing, which is rarely true, so start at whichever line matches the gap in what you already have.
| Trips per year | Typical trip length | Buy first | Buy second, if at all |
|---|---|---|---|
| 1 to 2 | 7 nights or more | Checked case, soft side | Cabin case only when the pattern changes |
| 3 to 5 | 3 to 7 nights | Cabin case | Checked case in year 2 |
| 6 or more | 2 to 4 nights | Cabin case, soft side | A second cabin case before any checked case |
| 6 or more | mixed, some long | Cabin case | Checked case within the first 12 months |
The ordering rule is simply that the case used on the most trips earns its price down fastest. Our budget guide divides a price by trips rather than by years for that reason.
Before you buy
- Find the baggage page for the airline you fly most and write down its three cabin dimensions and its weight cap
- Measure any case you already own over the wheels and the retracted handle, not over the shell
- Weigh the empty case on a bathroom scale and subtract it from the cap to get your real contents allowance
- Turn the case over and confirm that wheels and the handle assembly are bolted rather than moulded in
- Check that the maker lists wheels, handle tubes and zip pulls as spare parts you can buy
- Decide whether a quart bag of liquids and a power bank can come out of the case without unpacking it
- Count your trips in the last 12 months before deciding whether the cabin or the checked case comes first
Questions readers ask
- Is a hard shell or a soft side better for a cabin bag?
- Soft sides win on allowance and hard shells win on protection. On a 22 lb cabin cap the example figures above leave 16.5 lb of contents in a 5.5 lb soft case against 14.5 lb in a 7.5 lb hard shell, which is about 14% more. If you carry a camera, bottles or anything that crushes, spend that 14% on the shell deliberately.
- Do the wheels count towards the published size?
- At a sizer frame they do, because the frame measures the extreme points of the case. That is why a spinner assembly standing 1.5 inches proud turns a 22 inch allowance into about 20.5 inches of packable body. Measure your own case over the wheels and the retracted handle with a tape and write that number down.
- Can I put a power bank in a checked bag if the case locks?
- No. The Transportation Security Administration states that spare, uninstalled lithium ion and lithium metal batteries, including power banks and battery charging cases, must travel in carry-on baggage only, and a lock makes no difference to that. Spares rated 101 to 160 Wh are additionally capped at two per passenger and need airline approval before the flight.
- How many litres do I actually need for a week?
- Around 38 litres of usable space covers seven days for most people once bulky items are worn rather than packed, which is what the 22 x 14 x 9 inch example row works out to at 85% packing efficiency. Below about 29 litres a week becomes a laundry plan rather than a packing plan.
- Is an expandable zip worth paying for?
- On a checked case it is useful, because the hold cap is a weight cap rather than a size cap and an extra 2 inches of depth can absorb what you bought on the trip. On a cabin case it is close to useless, because expanding it puts the case outside the sizer frame that allowed it on in the first place.
Sources
- Transportation Security Administration — travel FAQ, carry-on size dimensions vary by airline — checked 2026-11-03
- Transportation Security Administration — lithium batteries over 100 watt hours in carry-on and checked bags — checked 2026-11-03
- Transportation Security Administration — liquids rule, 3.4 ounces per container in one quart-sized bag — checked 2026-11-03
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