A common problem: you buy a suitcase, and you're not sure whether it counts as carry-on, how many days it's suitable for, or how many outfits it can hold. This guide covers every commonly searched luggage size from 18 to 32 inches, plus a full comparison of carry-on allowances across Thai airlines, all in one place.

Suitcases are generally grouped into three categories: small (18-20 in) for carry-on or short trips, medium (22-26 in) for typical 5-12 day trips, and large (28-32 in) for long trips or family travel. The "inch" number refers to the bag's height, not its diagonal or combined dimensions.

Figures below are approximate industry averages, since exact dimensions vary slightly by brand — always double-check the specific bag's actual spec.

The standard cabin allowance most Thai airlines use is 56 x 36 x 23 cm (22 x 14 x 9 in), max 7 kg. Most 20-inch bags fall within this. 22-inch bags sit in a gray zone — some pass, some don't, depending on the brand's exact proportions. Anything 24 inches or above always exceeds cabin limits on every airline and must be checked.

Checked bags are typically measured by the sum of all three dimensions (width + length + height), not per side, capped at 158 cm. Most 28-30 inch bags still fall within this, but some 32-inch bags exceed it, triggering an oversized-baggage fee on top of the normal weight charge.

This question usually confuses "how much the bag can physically hold" with "how much weight the airline allows." In practice, weight is governed by your ticket's checked-baggage weight quota, typically 20-30 kg per piece depending on the airline and fare — not by the bag's inch size directly. A 20-inch bag used as carry-on is instead capped at 7 kg under cabin rules, unrelated to checked weight quotas.

Backpacks and non-wheeled bags are usually sized in liters instead of inches. Roughly: a 20-30L backpack is comparable to an 18-20 inch suitcase — fine for a day trip or as a second bag. A 40L backpack is often within 56x36x23 cm and can usually be carried on, though some models run taller than expected, so check the actual spec. A 50-60L backpack is comparable to a 24-26 inch suitcase and usually must be checked. A 90L backpack or bag is very large — equivalent to a 28-30 inch suitcase — and must always be checked.

Nearly every airline allows a second bag separate from your main carry-on — a laptop bag, sling bag, or handbag. It's usually much smaller, and some airlines count its weight together with the main bag. Knowing this in advance helps you pack smarter, since heavier items can go into the small bag you keep on you.

If your bag exceeds the size or weight limit at the gate, staff will usually give you two options: pay a gate check-in fee (almost always more expensive than buying extra weight online in advance), or remove some items before boarding. Both cost time and can risk missing your flight if the gate is about to close.

Use a tape measure and include wheels and handles that protrude from the bag, since airlines measure the full protruding dimensions, not just the shell. Measure width (narrowest side), length (front face), and height (including wheels and handle), then add all three together to compare against the 115 cm (cabin) or 158 cm (checked) threshold, whichever applies.

If you're flying multiple airlines on one trip, pack to the smallest size limit among them so you're never at risk of a re-check. Always weigh your bag at home with a digital luggage scale before you leave, and put heavy items like shoes or books into your second bag if the airline doesn't count its weight together with the main one. Soft-shell, compressible bags tend to handle slightly-over-the-limit situations better than hard-shell ones.

Three main groups: small 18-20 in (carry-on/short trips), medium 22-26 in (5-12 day trips), and large 28-32 in (long trips/family). See the full chart above for details on each size.

No. A 24-inch bag exceeds the standard cabin allowance (56x36x23 cm) on every airline and must always be checked.

Usually yes, since most 20-inch bags fall within 56x36x23 cm. Still, double-check your specific bag's actual dimensions, as some models run slightly taller or deeper than expected.

Any bag 25 inches or larger must be checked — it cannot be used as cabin carry-on. A 30-inch bag can be checked normally as long as the sum of its three dimensions is under 158 cm and its weight fits your ticket's quota.

Yes — this size is well under the standard cabin limit, so it's accepted as carry-on on every airline.

Approximately 22 x 14 x 9 inches — the standard cabin size most low-cost carriers in Thailand use. Thai Airways allows a slightly larger 56 x 45 x 25 cm.

158 cm doesn't convert directly to a single inch measurement because it's the sum of three sides, not one — roughly equivalent to about 62 inches combined. This threshold applies to checked baggage; exceeding it triggers an oversized-baggage fee.

As carry-on, it's capped at 7 kg under cabin rules, unrelated to the bag's actual capacity. In terms of packing space, a 20-inch bag typically fits about 4-6 outfits for a 2-4 day trip.

Around 5-10 days, holding roughly 8-10 outfits. It's the size most travelers default to since it fits typical trips without being too bulky.

A 20-30L backpack is comparable to an 18-20 inch suitcase and can normally be carried on. A 40L backpack can often be carried on too if it's within 56x36x23 cm, but check the actual spec. A 90L bag or backpack is very large — equivalent to a 28-30 inch suitcase — and must always be checked.

Thai AirAsia and Thai Vietjet both use the standard 56x36x23 cm (about 22x14x9 in). Thai Airways allows a larger 56x45x25 cm. Scoot sets a slightly smaller 54x38x23 cm. See the full airline comparison table above for every carrier.

No. Even when the numbers look similar, details differ — such as whether the second bag's weight is combined with the main bag, and airlines like Bangkok Airways that vary allowance by aircraft type.

Measure your actual bag with a ruler or tape measure at home before you travel, compare it against the table above for your specific airline, and check the airline's official page again closer to your travel date, since policies can change.

Data in this article is sourced from each airline's own official website and general market averages for luggage dimensions at time of publishing. Actual sizes vary slightly by brand, and airline policies can change — always verify with the airline again before you travel.