What's the Best Size for a Travel Backpack?

What's the Best Size for a Travel Backpack?

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

Most backpacks are between 20 and 85 liters. That range is huge. So what size is best for traveling?

Small bags, starting around 20L, are best used as daypacks. They work well when you’re only carrying a few items that you need to keep handy, like a light jacket, a camera, or snack. Twenty-five liter bags can also be used for short weekend trips if you’re a light packer.

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

But bags larger than 65L are way 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 anyway. You can’t—or at least shouldn’t—try to carry a month’s worth of dirty clothes.

Between these two extremes is the sweet spot of backpack sizes. A 30-40L backpack is perfect for travel. Keep reading to learn why and how this size can save you money.

The Best Size is Carry On Size

If you have to check your bag, you’ll pay checked bag fees, wait around at baggage claim, and risk lost or damaged luggage. Instead, travel carry-on-only.

The ideal travel backpack is carry-on-sized for:

  • Easy transport: Smaller is lighter. 
  • Avoiding baggage fees: Save $50 per roundtrip flight.
  • Downsizing your luggage: Packing light can be hard, so self-imposed constraints can be a good thing.
  • Preventing airlines from mishandling or losing your bag: Keep it on the plane and in your hands, not theirs.

Airlines’ carry on limits are either defined in volume (liters) or dimensions (inches). Some airlines also publish weight limits.

  • Volume: A 45L backpack is the maximum-size allowed on most US airlines. For international or budget airlines, choose a bag 40L or less. If you want to pack ultralight, anything 35L or under can be carried on virtually any airline and, in some cases, will even fit under the seat.
  • Dimensions: The common 45L volume is usually measured as 22 x 14 x 9 inches. You might also see a limit of 45 linear inches. Linear inches are the sum of the dimensions: length + width + height. The international max is 55 x 35 x 20 cm.
  • Weight: Most airlines allow bags up to 22 lbs (10 kg). Budget airlines are stricter and may charge you for the extra weight or force you to check your bag and pay the baggage fees.

Airlines will vary by volume, dimensions, or weight. The above are good rules of thumb, but always check your airline’s rules before flying to avoid any last-minute surprises.

Bags larger than 45L cannot be carried on. If you see a 50L backpack marketed as a carry oncarry on, double-check the dimensions. It’s probably too big to qualify as cabin luggage. Most airlines won’t measure your bag or look too closely at it if it’s near to the limits. But we recommend obeying the rules so that you never have to worry about whether you’ll sneak by the gate agent or not.

Packing carry-on-only might seem daunting at first, but packing for a long trip in a carry on backpack is totally doable with a little preparation.

The Right Size of Travel Backpack

I learned all this back in 2009 while researching bags for my first backpacking trip to Europe. I was surprised to discover that most backpacks were too big to be carried onto a plane. Large backpacks were mostly made by outdoor companies without regard for carry on rules. No one was designing bags for city travelers like me.

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

Every backpack that we make is a carry oncarry on. Even when fully packed, the max dimensions for our 40L bags exactly match the size that most international airlines allow so you never have to worry about checking your bag.

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