How Do I Know What Size Backpacking Bag to Get: Your Ultimate Guide to the Perfect Fit

Standing in the outdoor gear aisle, staring at a wall of backpacks, can be a genuinely daunting experience. You’ve got your hiking boots, your tent is practically begging to be used, and now you’re faced with this crucial decision: what size backpacking bag to get? I remember my first time, feeling completely overwhelmed. The numbers – liters, cubic inches – all swam before my eyes, and I honestly had no clue where to begin. I ended up with a bag that was far too large, leading to overpacking and unnecessary strain on my back during my maiden voyage. That’s precisely why understanding how to choose the right size backpacking bag is so incredibly important. It’s not just about hauling your gear; it’s about ensuring comfort, efficiency, and ultimately, the enjoyment of your outdoor adventures.

The Fundamental Question: Size Matters, But How Much?

So, how do I know what size backpacking bag to get? The answer isn’t a single, magic number. Instead, it’s a carefully considered decision based on several key factors, primarily the duration and type of your trip, as well as your personal packing style. For a quick weekend getaway, you’ll need a significantly smaller pack than for a month-long trek through the wilderness. Think of it like packing for a day trip versus a move across the country; the container size naturally adjusts to the volume of your belongings. The goal is to find a backpack that can comfortably hold all your essentials without being excessively bulky or forcing you to leave crucial items behind.

Understanding Backpack Capacity: Liters Explained

Backpack capacity is almost universally measured in liters. This is a standard unit of volume, and it’s your primary guide when determining the right size. However, it’s essential to understand what these numbers actually represent in terms of real-world gear. A general rule of thumb is that more liters mean more space, but it’s not always a linear relationship. You’ll see packs ranging from as small as 30 liters for ultralight day hikes or minimalist overnight trips, all the way up to 85 liters or more for extended expeditions. It’s easy to get caught up in the biggest is best mentality, but that’s a common pitfall. An oversized pack often tempts you to bring more than you need, adding unnecessary weight and bulk, which can truly detract from your experience.

Key takeaway: Liters are your primary measurement, but context is everything. Consider the trip length and your gear before focusing solely on the liter count.

Factors Influencing Your Backpack Size Choice

Before you even start looking at specific models, you need to assess your typical backpacking habits. This self-assessment is the most critical step in figuring out how to know what size backpacking bag to get. Let’s break down the elements that will guide your decision:

Trip Duration: The Most Significant Variable

This is arguably the biggest determinant of your backpack’s required capacity. Short trips need less gear, and therefore, less space. Longer trips necessitate more food, fuel, clothing, and potentially specialized equipment, all of which demand more volume.

Overnight (1-2 nights): For a single overnight or a short weekend trip, you can typically get away with a smaller pack. Think 30-45 liters. This is for those who are efficient packers and have a compact gear setup.
Weekend (2-3 nights): This is the sweet spot for many casual backpackers. A 45-60 liter pack is usually sufficient to comfortably carry essentials for a couple of days, including a bit more food and possibly an extra layer of clothing.
Multi-day (3-5 nights): As you extend your trips, your food and fuel needs increase substantially. A pack in the 60-75 liter range becomes more appropriate here. You’ll have enough room for more substantial meals and the associated weight.
Extended Trips (5+ nights): For week-long adventures or longer, you’re looking at the larger end of the spectrum. Packs in the 70-85+ liter range are common for those embarking on thru-hikes or extended backcountry expeditions where resupply points are few and far between.
Winter Backpacking: It’s crucial to note that winter backpacking adds another layer of complexity. You’ll need bulkier insulation, larger sleeping bags, and potentially more fuel. A good rule of thumb is to add 5-10 liters to your typical capacity for winter conditions.

Your Packing Style: Minimalist vs. Comfort Seeker

Are you the type of person who meticulously weighs every ounce and chooses the lightest possible gear, or do you prefer to bring a few extra comforts to make your trip more enjoyable? Your packing style directly impacts how much space you’ll need. I, for one, have learned over the years to lean towards the more minimalist side, but I still appreciate a few creature comforts. It’s a balancing act, for sure.

Ultralight/Minimalist: If you’ve invested in ultralight gear (think down sleeping bags, inflatable sleeping pads, minimalist tents), you can get away with a smaller pack, even for longer trips. Your total gear weight might be under 20 pounds, allowing for a pack in the 40-55 liter range for extended trips.
Moderate Packer: This is the most common category. You have a good balance of efficient gear but aren’t obsessed with shedding every last gram. You might bring a compact tent, a synthetic or down sleeping bag, and a comfortable sleeping pad. A 55-70 liter pack is likely your sweet spot.
Comfort-Oriented Packer: If you prioritize comfort and don’t mind a bit of extra weight, you might bring a more robust tent, a thicker sleeping pad, extra clothing layers, a camp chair, or a larger pillow. You’ll probably need a pack in the 70-85+ liter range, especially for longer trips.

The Type of Gear You Use: Packed vs. Bulky

The compressibility and size of your gear play a significant role. For instance, a down sleeping bag that stuffs into a tiny sack takes up far less space than a bulky synthetic bag. Similarly, a lightweight tent that collapses small will leave more room than a heavier, more structured one.

Compressible Gear: Down sleeping bags, inflatable sleeping pads, and modern, compact tents generally require less space.
Bulky Gear: Older synthetic sleeping bags, thick foam sleeping pads, and larger, more structured tents will demand more volume. Consider if you’re bringing items like an axe, snowshoes, or bulky photography equipment. These items can significantly increase the volume you need to carry.

Specific Activities and Environments

Certain activities or environments might necessitate specialized gear that takes up more space. For example:

Climbing/Mountaineering: You might need to carry ropes, a helmet, ice axes, and crampons, all of which can be bulky.
Winter Camping: As mentioned, bulkier insulation, sleeping bags, and larger stoves are typically required.
Photography/Videography: If you’re a photographer, you’ll likely need to pack a camera body, multiple lenses, batteries, and accessories, which can significantly increase your volume needs.

Backpack Sizing by Volume: A General Guideline

To help you visualize, here’s a table that provides a general overview of backpack volumes based on trip length and packing style. Remember, these are starting points, and your personal needs might vary.

Trip Duration	Ultralight Packer (Liters)	Moderate Packer (Liters)	Comfort Packer (Liters)	Winter/Specialty Gear (Liters)
Overnight (1-2 nights)	30-40	40-50	45-55	N/A (Typically longer trips)
Weekend (2-3 nights)	40-50	50-60	55-65	55-65
Multi-day (3-5 nights)	50-60	60-70	65-75	65-75
Extended Trip (5+ nights)	60-70	70-80	75-85+	75-85+

Important Note: This table is a guideline. If you’re an ultralight packer, you might be able to get away with a smaller pack than listed. Conversely, if you pack a lot of comfort items or specialized gear, you might need a larger pack. Always consider your personal gear and trip specifics.

Beyond Volume: Torso Length and Fit Are Paramount

While volume is the primary indicator of how much your bag can hold, it’s not the only sizing factor. In fact, for comfort and proper weight distribution, **torso length is arguably more important than volume when it comes to how a pack will feel on your back.** A backpack that is the correct volume but the wrong torso length will be incredibly uncomfortable, regardless of how well you pack it. This is where many people, myself included in my early days, make a critical mistake. You might have the perfect liter capacity, but if the pack isn’t fitted to your body, it’s going to cause issues.

Why Torso Length Matters

Backpacks are designed with adjustable suspension systems. The shoulder straps connect to a frame, and the hip belt is crucial for transferring the majority of the pack’s weight from your shoulders to your hips. If the pack is too long or too short for your torso, this weight transfer won’t happen effectively. Instead, you’ll feel the weight pulling down on your shoulders, leading to pain, fatigue, and a generally miserable hiking experience. This is why you’ll often see backpacks offered in different torso sizes (e.g., Small, Medium, Large) or with an adjustable torso length mechanism.

How to Measure Your Torso Length

Measuring your torso length is straightforward and can be done at home. You’ll need a flexible measuring tape and a friend to help, or you can do it yourself with some careful maneuvering.

Locate Your C7 Vertebra: This is the most prominent bone at the base of your neck when you tilt your head forward. It’s usually easy to feel.
Locate Your Iliac Crest: This refers to the top of your hip bones. Imagine a line drawn straight across your back, connecting the highest points of your hip bones.
Measure the Distance: With your head tilted forward, have your helper (or carefully yourself) run the flexible tape measure from the C7 vertebra straight down your spine to that imaginary line across your iliac crest. Keep the tape snug but not digging in.

The measurement you get, typically in inches or centimeters, will correspond to a size range offered by most backpack manufacturers. For example:

Men’s Packs: Small (16-18 inches), Medium (18-20 inches), Large (20-22 inches)
Women’s Packs: Small (15-17 inches), Medium (17-19 inches), Large (19-21 inches)

Crucial Tip: Always consult the specific sizing chart of the backpack brand you are interested in. While these ranges are common, there can be slight variations between manufacturers.

Selecting a Backpack: The Practical Steps

Now that you understand the importance of volume and torso length, let’s walk through the process of actually choosing and fitting a backpack.

Step 1: Determine Your Primary Trip Type and Duration

As we’ve discussed, start by thinking about the majority of your backpacking trips. Are they mostly weekend excursions? Are you planning on a week-long trek in the Sierras? This will give you a target volume range.

Step 2: Assess Your Gear and Packing Habits

Take a realistic look at your current gear. Is it lightweight and compressible, or is it older and bulkier? Are you someone who likes to bring a book, a camera, or other non-essential but enjoyable items? This will help you refine your volume estimate. If you’re unsure, it’s often better to err slightly larger than too small, but avoid going excessively large. An extra 5-10 liters can usually be managed with good packing techniques.

Step 3: Measure Your Torso Length

Follow the steps outlined above to get an accurate torso measurement. This is non-negotiable for a comfortable pack. Don’t guess!

Step 4: Research Backpack Models within Your Target Range

Once you have a target volume (e.g., 60-70 liters) and know your torso size, start looking at specific backpack models. Read reviews, watch videos, and pay attention to features that are important to you (e.g., hydration reservoir compatibility, number of pockets, ease of access to compartments).

Step 5: Try Before You Buy (Essential!)

This is the most critical step. You absolutely must try on backpacks before you purchase them. If possible, visit an outdoor gear store that specializes in backpacking equipment. Here’s what to do:

Ask for Help: Don’t be shy. Let the store associates know your intended use and that you need help with fitting.
Load the Pack: A backpack won’t feel the same empty as it will when loaded. Ask the store to put some weight in the pack – typically around 15-25 pounds for initial fitting. They usually have sandbags or weights for this purpose.
Adjust the Torso (if applicable): Ensure the torso length is set correctly for your measurement.
Loosen All Straps: Before putting the pack on, loosen the shoulder straps, load lifters, sternum strap, and hip belt.
Put on the Pack: Step into the hip belt. It should sit comfortably on your iliac crest, directly on top of your hip bones. Tighten the hip belt snugly. This is where the majority of the weight should rest.
Tighten Shoulder Straps: Pull the shoulder straps down and back. They should curve over your shoulders without any significant gaps.
Connect and Adjust the Sternum Strap: This strap goes across your chest and helps stabilize the pack and prevent the shoulder straps from slipping off. Adjust it for comfort.
Adjust Load Lifters: These are the small straps that connect from the top of the shoulder straps to the top of the pack frame. They should be at about a 45-degree angle to the pack. Tightening them pulls the top of the pack closer to your body, helping with balance and comfort.
Walk Around: Spend at least 10-15 minutes walking around the store with the pack on. Go up and down stairs if possible. Pay attention to any pressure points, rubbing, or discomfort. Does the pack move with you? Does it feel balanced?

Step 6: Consider Frame Type and Features

While focusing on size and fit, also consider the type of frame and features offered:

Internal Frame Packs: These are the most common type today. The frame is integrated within the pack, providing support and structure while keeping the pack close to your body for better balance.
External Frame Packs: Less common now, these have a visible frame structure outside the pack. They tend to be more adjustable and can offer better ventilation but are often heavier and can snag on branches.
Features: Think about what you need. Do you want a top-loading pack with a lid, or do you prefer a panel-loading pack with a zippered front for easier access? Do you need a separate sleeping bag compartment? How many external pockets do you want for water bottles or snacks?

Common Mistakes to Avoid When Choosing Backpack Size

I’ve seen and made my fair share of mistakes when it comes to backpack selection. Learning from them can save you a lot of pain and frustration on the trail.

Buying Too Big: As I mentioned earlier, the temptation to get a larger pack “just in case” is strong. This often leads to overpacking, which means carrying unnecessary weight. A heavier pack is harder to hike with, less enjoyable, and can increase your risk of injury. A pack that’s too big can also feel awkward and unstable.
Not Measuring Torso Length: This is a cardinal sin of backpack fitting. Relying on general clothing sizes (S, M, L) for a backpack is a recipe for disaster. Your torso length is the key to proper fit and weight distribution.
Assuming All Packs Fit the Same: Different brands have different suspension systems, harness designs, and torso adjustments. What works for one brand might not work for another. Always try them on.
Not Trying the Pack On with Weight: An empty pack is a poor indicator of how it will feel on the trail. Always try it on with a significant amount of weight to simulate real-world conditions.
Prioritizing Features Over Fit: While cool pockets and integrated rain covers are nice, they are secondary to a comfortable, well-fitting pack. If the pack doesn’t fit, all those fancy features won’t make up for it.
Not Considering Your Gear: If you have bulky gear, a smaller pack will be a struggle. Conversely, if you have an ultralight kit, a massive pack will feel like overkill and be difficult to manage.
Relying Solely on Online Reviews: Online reviews are helpful for general impressions and feature analysis, but they cannot replace the experience of trying a pack on your own body.

Special Considerations for Different Types of Backpacks

While this article primarily focuses on backpacking packs, it’s worth noting that other types of packs have different sizing considerations:

Daypacks: These are much smaller (15-30 liters) and are designed for shorter excursions. Fit is less critical for torso length, as the weight is usually distributed to the shoulders, but a comfortable harness is still important.
Travel Backpacks: These often prioritize organization and accessibility over the complex suspension systems of true backpacking packs. While they might have adjustable torso lengths, the emphasis is more on carrying capacity and ease of use in urban environments.
Hydration Packs: These are small packs designed to carry a water reservoir and a few essentials. They are typically worn snugly and have minimal padding.

Frequently Asked Questions About Backpack Size

Here are some common questions I hear from people trying to figure out what size backpacking bag to get, along with detailed answers:

Q: I’m planning a 3-day hike. Should I get a 50-liter or a 65-liter pack?

This is a classic dilemma! For a 3-day hike, the answer really hinges on your packing style and the type of gear you’ll be bringing. If you’ve invested in ultralight and compressible gear, and you’re meticulous about packing efficiently, a 50-liter pack might be perfectly adequate. You’ll need to be strategic about how you pack, perhaps using compression sacks for your sleeping bag and clothing. However, if you’re a more moderate packer, or if you anticipate needing extra layers due to changing weather, or if you simply prefer a bit more comfort and space, a 65-liter pack would likely be a better choice. It offers more breathing room, reducing the stress of trying to cram everything in. Furthermore, a slightly larger pack can sometimes be easier to manage if you need to stash something on the outside temporarily. My personal advice? For a 3-day trip, unless you are a seasoned ultralighter, I’d lean towards the 65-liter pack. It’s better to have a little extra space that you can manage than to constantly struggle with a pack that’s too small. Remember, the goal is comfort and enjoyment on the trail, and wrestling with an overstuffed pack can really detract from that.

Q: How do I know if a backpack’s torso size is correct for me?

This is where the physical fit comes into play, and it’s absolutely crucial. A backpack’s torso size is correctly matched to you when the hip belt sits directly on top of your iliac crest (your hip bones), and the shoulder straps curve comfortably over your shoulders without any significant gaps. When you put the pack on and tighten the hip belt, the majority of the pack’s weight (around 80%) should feel like it’s resting on your hips, not pulling down on your shoulders. The shoulder straps should feel snug and supportive, but not so tight that they’re digging into your armpits or restricting your movement. The load lifter straps, which connect from the top of the shoulder straps to the top of the pack frame, should be at about a 45-degree angle when snugged. They help pull the pack closer to your body and transfer some of the remaining load to your shoulders. If you feel pressure points, pinching, or rubbing anywhere, or if the pack feels like it’s swaying independently of your body, the torso size is likely not correct. This is why trying on a pack with weight is so important; an empty pack can mask fit issues.

Q: Can I use a large backpacking bag for a short trip?

Yes, you absolutely *can* use a large backpacking bag for a short trip, but it’s generally not recommended, and here’s why. A backpack that’s too large for the amount of gear you’re carrying can be problematic. Firstly, it tempts you to overpack. You’ll find yourself filling up all that extra space with items you don’t really need, which adds unnecessary weight. Secondly, a partially full, large pack can be unstable. It might lack structure, causing your gear to shift around inside, which can throw off your balance on uneven terrain. This instability can make hiking more tiring and increase the risk of a fall. Finally, a large, bulky pack can feel cumbersome and unwieldy, even if it’s not fully loaded. It might snag on branches more easily, and it can just feel generally awkward. While you *can* cinch down all the compression straps to make a larger pack more manageable, it’s never as efficient or comfortable as using a pack that’s appropriately sized for your load. If you find yourself consistently using a large pack for short trips, it’s probably time to invest in a smaller pack specifically for those excursions.

Q: What’s the difference between men’s and women’s backpacking bags, and does it matter for size?

Yes, the difference between men’s and women’s backpacking bags is significant, and it absolutely matters for fit and comfort. These differences are primarily based on typical anatomical variations between sexes. Women’s backpacks are generally designed with:

Shorter Torso Lengths: As we’ve discussed, women often have shorter torso lengths, so women’s packs often have shorter torso size ranges.
Narrower Shoulder Width: Women’s shoulder straps are often contoured to be narrower and might have a more S-shaped curve to accommodate a typically narrower shoulder width and avoid chafing under the arms.
Shaped Hip Belts: Women’s hip belts are often designed with a more conical shape to better contour to a typically more pronounced curve in the hips.
Adjustable Sternum Straps: While both types have sternum straps, women’s versions are often designed to be positioned higher or have more adjustability to accommodate natural curves and avoid pressure on the bust.

Men’s packs, conversely, are typically designed for longer torsos, wider shoulders, and straighter hip belts. While some unisex packs exist, they often compromise on the nuances of fit. For most women, a women’s specific pack will offer a far superior and more comfortable fit, especially when dealing with heavier loads. For men, a men’s pack will generally provide the best fit. It’s not just about aesthetics; it’s about engineering the pack to fit the average human anatomy for optimal load-bearing. If you’re an individual who falls outside the typical anatomical norms for your sex, you might find a pack from the other category fits you better, but always prioritize fit over gender labeling.

Q: How important are external pockets and features when choosing backpack size?

External pockets and features are important for organization and accessibility, but they are secondary to the overall size and fit of your backpack. Think of them as enhancers to your chosen size, not determinants of it. For example, a pack with lots of external pockets can help you keep frequently used items (like water bottles, snacks, a map, or rain gear) easily accessible, which can make a pack *feel* like it’s carrying less because you don’t have to dig through the main compartment. However, these pockets also add a small amount of bulk and weight themselves. When considering features, think about what will genuinely enhance your hiking experience:

Water Bottle Pockets: Are they large enough for your bottles? Are they easy to reach while wearing the pack?
Lid Pockets: Great for maps, headlamps, first-aid kits, and snacks.
Hip Belt Pockets: Excellent for small essentials like lip balm, a multi-tool, or energy gels.
Front Stretch Pocket: Ideal for stashing a wet rain fly or a jacket you need to shed quickly.
Hydration Reservoir Sleeve: Essential if you prefer drinking from a bladder.
Gear Loops and Straps: Useful for attaching trekking poles, ice axes, or a sleeping pad externally.

While these features are valuable, they don’t change the fundamental volume requirement of your pack. A well-organized pack with good features will feel more efficient, but if the core volume is wrong or the fit is poor, those features won’t compensate. Prioritize getting the right volume and torso fit first, and then choose a pack within that category that offers the features you’ll use most.

The Future of Backpacking Gear and Size Considerations

The world of outdoor gear is constantly evolving, and this absolutely includes backpacks. We’re seeing a continued trend towards lighter, more durable, and more packable materials. This push for ultralight gear means that in the future, you might be able to comfortably fit more gear into a smaller volume pack than you can today. Innovative designs, like frameless packs for minimalist hikers or packs made from advanced composite materials, are pushing the boundaries of what’s possible.

For consumers, this means that staying informed about new technologies and materials will continue to be beneficial. However, the fundamental principles of sizing – trip duration, packing style, and, most importantly, torso length for fit – will remain constant. Even with the most advanced gear, a poorly fitted pack will still be a burden. The key will always be finding the right balance for *your* needs, *your* gear, and *your* body. The pursuit of the perfect backpacking bag size is an ongoing journey, but with a solid understanding of the principles, you’ll be well-equipped to make the right choice.

Final Thoughts on Choosing Your Backpack Size

Figuring out how to know what size backpacking bag to get might seem like a complex puzzle at first, but by breaking it down into manageable steps, it becomes much clearer. It’s a combination of understanding your needs—how long your trips typically are, what kind of gear you carry, and how you like to pack—and understanding your body—specifically, your torso length. Remember, volume is your guide to capacity, but fit is your guide to comfort and usability on the trail. Don’t underestimate the power of trying on a pack with weight, adjusting all the straps, and walking around to feel how it truly behaves. It’s an investment, both in terms of money and in your future hiking experiences, so taking the time to get it right is absolutely worthwhile. Happy trails!

How Do I Know What Size Backpacking Bag to Get: Your Ultimate Guide to the Perfect Fit