Trips of 5 days or more usually call for packs of 70 liters or more. These are also usually the preferred choice for winter treks lasting more than 1 night. (Larger packs can more comfortably accommodate extra clothing, a warmer sleeping bag and a 4-season tent, which typically includes extra poles.)

For a one-week trip, the ideal backpack size is typically between 35 and 45 liters. This range is widely considered the "sweet spot" for travelers who want to avoid checking luggage while still having enough room for a week’s worth of essentials. A 40L bag is generally the maximum size allowed as a "carry-on" by most major international airlines. If you are a minimalist or traveling to a warm climate where clothes are thinner, you can easily manage with a 30-35L bag. However, if you need to carry extra shoes, a laptop, or bulkier layers for cold weather, a 45L bag provides that necessary extra margin. It is important to look for a bag with a "clamshell" opening (opens like a suitcase) rather than a top-loading hiking pack, as this makes accessing your clothes much easier during a hotel stay. Using packing cubes can also help you compress your items, allowing you to fit more into a smaller-volume bag while keeping your gear organized and preventing the "bottomless pit" effect common in larger backpacks.