How Many Liters Do You Need for a Trip?

Liters and airline limits are unrelated

Start here, because it overturns the assumption most people shop with. Airlines publish a box — height, width and depth. They do not publish a volume. A bag satisfies the rule by fitting inside the box, and how much it holds inside that box is entirely up to how well it is shaped.

The 45 L bag passes everywhere and the 35 L bag does not, because the smaller bag is an inch deeper. Ten liters of capacity is worth nothing at a sizer; one inch of depth is worth everything. What the carry-on box works out to in liters does the conversion the other way.

The capacity ladder

With that caveat established, here is what each band is actually for. Every figure below is a manufacturer-published capacity, and every bag named is one we track.

20 to 25 L — a day, or a personal item

Enough for a laptop, a jacket, lunch and a water bottle. This is a daypack, not a travel bag, and the Osprey Daylite Plus publishes 20 L at 1.31 lb for $80.

Watch the box rather than the volume if you intend to use it as a free personal item: it publishes 19 in of height against the 18 in that Frontier and Allegiant publish. Bags actually built to a personal-item box.

30 to 35 L — a long weekend

Two or three days of clothes, plus shoes. The Cotopaxi Allpa publishes 35 L at 2.93 lb, the lightest travel pack in our ledger.

This band is genuinely nicer to carry than 40 L and genuinely more limiting. If you are disciplined it is the sweet spot; where 30 to 35 L makes sense covers the trade.

40 to 45 L — a week, or a month

The one-bag standard, and the largest volume you can generally carry on. The Farpoint publishes 40 L at 3.27 lb; the Daylite Duffel publishes 45 L at 1.4 lb.

The important point is that this band does not run out at a week. With laundry it covers a month just as well, because clothing stops scaling with trip length once you wash. A month in a carry-on works through that.

60 L and up — you are checking a bag

Above about 50 L nothing clears a carry-on box, so the question changes from “will it fit the bin” to “will it fit 62 linear inches”, which is a different test entirely.

The Eagle Creek Cargo Hauler Wheeled 110 publishes 108 L at 4.25 lb and 59 linear inches — the most capacity we track inside the checked limit, at the lowest empty weight. Every large bag, added up.

At this size the binding constraint is usually weight rather than volume. A 50 lb checked cap that includes the bag means an 11 lb case has already spent a fifth of your allowance on itself.

How to choose in practice

• Work out your laundry interval first. It sets the clothing volume, and trip length does not.
• Then check the published box, not the liters. Depth is the dimension that fails bags. The published limits at every carrier.
• Buy the smaller one if you are between bands. A bag you fill is easier to carry than a bag you half fill, and a half-filled soft bag sags into a shape a sizer likes less.
• Ignore capacity entirely for checked bags. Linear inches and the weight cap decide it — how linear inches work.

And treat published volumes as approximate between brands. There is no standard method for measuring a bag’s interior, so one maker’s 40 L is not necessarily another’s. Dimensions are measured the same way by everyone; liters are not. What luggage size labels actually mean.