Whether you are an avid trekker or a student whose longest hike is across your college’s campus, the backpack style that you choose can, quite literally, make or break your back. If you are in the market for a new backpack you will find yourself faced with hundreds of choices and styles. Between internal frames and external frames, padded straps and cubic inches of packing space, there is a lot more to consider than simply the aesthetic appeal of a backpack. The question is how do you decide which backpack is the best backpack style for you?

The best way to determine which backpack to buy is to ask yourself a series of questions to narrow down your choices.

Why do you need a backpack?

The first question that you need to answer is why you need a backpack in the first place? How will you use it? A backpack that would be used to carry all of your belongings on a trek across Europe should offer far different features than one that is used to carry diapers and formula for your daily runs around town. Likewise, if you are heading out on a long distance trip through mountainous terrain or the woods, you could benefit greatly from bringing along a pack that can carry a lot of equipment comfortably without being too heavy.

A day pack is meant for light trekking, when carrying a lot of gear and weight is not an issue. If your main use for a backpack is to haul stuff around with you for use during the day, then a day pack like the Travel Gear Ur Gear Backpack will work just fine. The DadGear Basic Black Diaper Backpack is a daypack with special features designed specifically for parents toting along an infant or toddler. Other daypacks are designed with students in mind and offer features like outside pockets for MP3 players and cell phones.

The second type of backpack is the assault pack, which is larger than a day pack to allow you to carry more gear. Assault packs often have a frame to help distribute weight more evenly across your back and shoulders. It is the kind of pack you want if you are planning on a full day trip, or a day trek up a mountain or into the woods.

A pack like the High Peak Black Diamond Backpack is the ideal compromise between a lightweight day pack and a full pack meant for longer expeditions. The High Peak Black Diamond features over 1,500 cubic inches of packing space, foam-padded shoulder straps and a chest and hip belt to help keep the pack attached to where it belongs on your body. It also includes hiking features like holders for a shovel, ice axe and snowboard. While it does not have an internal frame, it does feature a removable aluminum support bar to give the backpack additional strength. Finally, it is compatible with hydration systems for packing along filtered water and making it easy to access while trekking.

If you are intending an all-out expedition lasting a week or more, then you should consider a full pack, which are backpacks that have room for all the gear you’ll need to survive in the woods for weeks. Most full packs have either an internal or an external frame, and can offer as much as 6,000 cubic inches of packing space. A full pack backpack like the High Peak Katmandu 70 + 10 Internal Frame Backpack may offer features like a full rain cover including hood to keep you and your gear dry in wet weather. Look for additional features like a bottom zipper to allow access to the bottom of the main compartment and multiple places to attach other gear on the outer backpack.

How does it fit?

Adjustable straps are all well and good, but some backpacks are a better fit than others. A backpack that does not fit comfortably can leave you with an aching back, or tire you out to the point where you have to quit hiking early. Some points to watch out for include:

• Chest straps that can help stabilize a heavy backpack, but may not be comfortable for most women because they fit across the chest.

• A foam padded back frame can fit the backpack snugly against your back, making it much easier to support.

• A hip belt, waist belt, or both are musts, but it is important that the belts hit the right place on your torso.

When choosing a backpack, measure your torso instead of your full height. If you are planning on doing a lot of backpacking, be sure to get a backpack that has a fully adjustable frame.

How much packing space do you need?

What can you fit into 1,000 cubic inches? How about 5,000 cubic inches? In general, the following rules of thumb apply:

• If you are selecting a pack for day trips or around the town use, then you should be fine with a day pack that has a capacity of up to 1,500 cubic inches. Kids’ backpacks can be proportionally smaller.

• If you plan on taking weekend trips or doing light backpacking and hiking, then you may want a backpack that’s substantially larger. A capacity of 1,750 to 3,000 cubic inches will provide plenty of packing room for clothes and gear for one person on a weekend camping trip.

If you are carrying gear for more than one person, or for an extended trip, look for a full pack with over 3,000 cubic inches of packing space. A full pack with an external frame will distribute weight evenly and make your backpacking trip a pleasure.