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What is the Best Size for a Travel Backpack?

Backpack and luggage sizing can be confusing, especially for Americans not used to measuring anything in liters. Visualizing thousands of cubic inches is impossible.

This article is your quick guide to understanding travel backpack sizes.

Most backpacks are between 25 and 85 liters. That range is huge.

Smaller bags, starting around 25L, are ideal for use as daypacks. They work well when you're only carrying a few items that you need to keep handy, like a light jacket, book, or camera. Twenty-five liter bags can also be used for short weekend trips if you're a light packer.

Very large bags, 65L and up, are for long hiking trips. These bags work well in the outdoors when you will be carrying multiple days worth of clothing and camping gear.

Bags larger than 65L are too big for travel, even on extended trips. If you'll be traveling for more than a week or two, you'll need to do laundry. Pack light, preferably in a carry on bag, and do laundry every few weeks. Don't carry your entire closet on your back.

Between these two extremes is the sweet spot for luggage size. Thirty-five to forty-five liter packs are ideal for travel. We recommend 45L.

The Best Size for a Backpack is Carry On Size

The ideal volume for a backpack is a function of its dimensions. Most airlines allow carry-on luggage up to 22" x 14" x 9". You may also see a limit of 45 linear inches (length + width + height). The ideal bag is carry-on-sized and takes full advantage of the airlines' size restrictions.

Unless you're a paragon of light packing, you'll want all the space you can get without having to check your bag.

A bag measuring 22" x 14" x 9" is 2,772 cubic inches in volume. Just multiply the three measurements together. 2,772 cubic inches translates to 45.2 liters.

A 45L bag is the most efficient use of your carry-on luggage allowance. It affords you the most packing space without having to check a bag.

Bags larger than 45L cannot be carried on. Take every inch the airlines will give you.
The ideal backpack is carry-on-sized for:

On budget airlines, make sure to weigh your bag, even if it is carry-on-sized. Most airlines allow bags up to 22 lbs (10 kg), but budget airlines are more strict and may charge you for the extra weight or force you to check your bag and pay the baggage fees.

While researching bags for a backpacking trip in 2009, we were surprised to discover that most backpacks were too large to be carried onto a plane. Large backpacks were mostly made by outdoors companies without regard for carry-on rules. No one had designed a bag for travelers.

The perfect travel backpack didn't exist; so we made it.

We designed the Outbreaker travel backpack to take full advantage of carry-on-baggage allowances. Even when fully packed, the Outbreaker’s max dimensions are 22" x 14" x 9".

Learn more about why the Outbreaker is the perfect backpack for city travel.