Standing in front of a wall of backpacks with numbers like 20L, 40L, and 65L can feel overwhelming when you are just trying to figure out what you need for your first real hike. The liter measurements seem arbitrary, the packs all look similar, and you are probably wondering whether you will end up with something too small that leaves your rain jacket dangling off the side or something so massive you look like you are preparing to climb Everest when you just want to walk a few miles on a Saturday morning.
The good news is that choosing the right pack size is more straightforward than it seems once you understand what those liter numbers actually mean and how they relate to the type of hiking you want to do. In this guide, we will break down pack sizing by trip type, show you what actually fits inside different capacities, explain why torso length matters more than your height, and give you the confidence to pick a pack that matches your hiking ambitions without overdoing it.
What to Look For
Understanding Liter Capacity and What It Really Means
When you see a pack labeled as 25L or 50L, that number refers to the total internal volume measured in liters—essentially how much stuff can physically fit inside all the compartments combined. To put this in perspective, a 20-liter pack is roughly the size of a large school backpack, while a 65-liter pack could hold everything you need for a week in the backcountry. The confusion for most beginners comes from not knowing how much gear different trip types actually require. A simple day hike where you are out for 4-6 hours needs far less than an overnight trip where you are carrying a sleeping bag, tent, and extra food.
Think about it this way: for a day hike, you typically need water (about 2 liters), snacks, a first-aid kit, a rain jacket, maybe an extra layer, sunscreen, and your phone. That collection of items fits comfortably in a 20-30 liter pack with room to spare. Once you start adding overnight gear—a sleeping bag alone takes up 8-12 liters, a tent adds another 10-15 liters, and a sleeping pad takes 3-5 liters—you quickly see why multi-day packs jump to 50 liters or more. The key is matching capacity to your actual needs, not buying the biggest pack available because it feels safer.
Pack Sizes by Trip Type: Day Hikes vs Overnight vs Multi-Day
For day hikes—trips where you start in the morning and return by evening without sleeping outdoors—a pack between 20-30 liters is ideal for most beginners. This size comfortably holds the Ten Essentials (navigation, sun protection, insulation, illumination, first-aid supplies, fire starter, repair kit, nutrition, hydration, and emergency shelter), plus personal items like your phone, keys, and wallet. A 25-liter daypack is the sweet spot for most people because it has enough room for an extra fleece if the weather turns but does not feel bulky or encourage you to overpack.
Overnight trips—one or two nights on the trail—typically require 40-50 liters of capacity. This range accommodates your sleeping bag, sleeping pad, a lightweight tent or shelter system, extra clothing for sleeping, additional food, a camp stove and fuel, and your water filtration system. Many beginner backpackers find that 45-50 liters works well because it provides enough space without being so large that you feel tempted to bring unnecessary items. The pack will feel substantial compared to a daypack, but when properly fitted and packed, it should ride comfortably on your hips rather than pulling on your shoulders.
For multi-day trips lasting 3-7 nights, you are looking at 50-70 liters depending on the season and your gear choices. Summer trips with lightweight gear can often work with packs in the 50-60 liter range, while winter trips or expeditions requiring bulkier clothing and a four-season tent push you toward 65-70 liters. As a beginner, if you are considering longer trips, starting with a 60-65 liter pack gives you flexibility as you dial in your gear and figure out what you actually need versus what you thought you needed.
Why Torso Length Matters More Than Your Height
This is where many beginners make their biggest mistake: they choose a pack based on their overall height or a generic small/medium/large sizing system without measuring their torso length. Your torso length—the distance from the bony bump at the base of your neck (your C7 vertebra) to the top of your hip bones—determines how the pack sits on your body and whether the hip belt lands in the right spot to transfer weight off your shoulders. A person who is 5 feet 8 inches tall might have a short torso if they have long legs, or a long torso if they have shorter legs, and those two people need completely different pack sizes.
To measure your torso length at home, tilt your head forward and feel for that prominent bone at the base of your neck. That is your starting point. Then place your hands on your hips and feel for the top of your hip bones—that is your ending point. Measure the distance between these two points, ideally having someone help you. Most packs come in torso length ranges: extra-small (15 inches or less), small (15-17 inches), medium (17-19 inches), and large (19 inches or more). Some packs have adjustable torso lengths, which can be helpful if you are between sizes or unsure of your exact measurement.
When a pack fits your torso properly, the hip belt sits directly on your hip bones (not above your waist or down on your butt), the shoulder straps attach just below the top of your shoulders without gaps, and the load lifter straps (small straps that angle from the top of the pack to your shoulder straps) pull at roughly a 45-degree angle. If any of these positions are off, the pack will not carry weight efficiently, and you will feel strain in your shoulders and lower back even on short hikes. Many outdoor retailers offer free pack fitting services, which is incredibly valuable for first-time buyers who want to get this right.
How to Test If a Pack Size Is Right for You
Before buying a pack, especially for overnight or multi-day trips, you should load it with weight and walk around the store or your home for at least 15-20 minutes. Many retailers keep sandbags or weighted items specifically for this purpose. Start by loosening all the straps, putting the pack on, and fastening the hip belt first—this is the most important strap because it should carry 80 percent of the pack weight. Tighten the hip belt so it is snug on your hip bones, then adjust the shoulder straps so they are snug but not bearing all the weight. Finally, tighten the load lifter straps and sternum strap.
Pay attention to several comfort indicators during your test walk. The pack should feel stable when you turn side to side or lean forward slightly, not swaying independently of your body. You should not feel pressure points digging into your hips, shoulders, or back. Your shoulders should not be taking all the weight—if they are, the hip belt is not positioned correctly or not tight enough. Also check that you can reach important features like side pockets for water bottles and hip belt pockets for snacks without having to remove the pack. If you feel discomfort during a 15-minute test with moderate weight, that discomfort will multiply dramatically over several hours on the trail with full gear.
Common Beginner Mistakes When Choosing Pack Size
The most common mistake beginners make is buying too large of a pack thinking they will grow into it or that more space is always better. The problem with an oversized pack is that it encourages overpacking—empty space begs to be filled, and you will likely bring items you do not actually need. A 65-liter pack for day hiking is like driving a moving truck to the grocery store: technically functional but unnecessarily cumbersome. The extra fabric, frame, and features also add weight even when the pack is empty, making your load heavier before you even add gear.
Another frequent error is prioritizing price over fit. A $50 pack that does not fit your torso will cause pain and potentially injury, while a $150 pack that fits properly will feel comfortable even with significant weight. Think of it this way: your pack is the single piece of gear that touches your body for the entire duration of every hike. Poor fit affects your entire experience, while good fit becomes invisible—you stop thinking about the pack and start enjoying the trail. If budget is tight, look for last season models on sale or quality used packs, but never compromise on proper fit to save money.
Finally, many beginners do not consider compression features and expandability. Some packs offer removable tops or compression straps that let you shrink a 50-liter pack down to 40 liters for lighter trips or expand it for heavier loads. This versatility can be valuable if you are planning to do both day hikes and occasional overnight trips, letting one pack serve multiple purposes rather than needing separate packs for each activity type.
Frequently Asked Questions
How big of a hiking pack should I get for my first backpack?
For your very first hiking backpack, a 20-30 liter daypack is the best choice if you are primarily planning day hikes. This size handles everything you need for trips up to 6-8 hours without encouraging overpacking. A 25-liter capacity is particularly versatile—large enough for extra layers and emergency gear, but small enough that it does not feel cumbersome on shorter trails. If you know you want to try overnight backpacking soon, consider starting with a 40-50 liter pack instead, which can work for both day hikes (just leave it partially empty) and handle your first overnight adventures. The important thing is to avoid buying a massive 65-liter pack right away unless you have specific plans for extended trips, as larger packs are heavier even when empty and make it tempting to bring unnecessary items that add weight and reduce your enjoyment on the trail.
What is the difference between a 30L and 50L backpack?
The difference between a 30L and 50L backpack is substantial in both capacity and intended use. A 30-liter pack is designed for day hikes and can hold your water, snacks, extra clothing layers, first-aid supplies, and emergency gear, but it cannot accommodate overnight camping equipment like a sleeping bag, tent, and sleeping pad. A 50-liter pack nearly doubles that capacity and includes space for all your camping gear plus food and cooking supplies for 1-2 night trips. The physical difference is also noticeable—50L packs typically have more robust frames, padded hip belts designed to carry heavier loads, and additional attachment points for external gear. They also weigh more when empty, usually 3-4 pounds compared to 1-2 pounds for a 30L daypack. If you are only planning day hikes, a 50L pack is excessive and will feel bulky. If you want to try overnight backpacking, a 30L pack is too small to fit your camping gear safely and comfortably.
Can I use a 50L backpack for day hikes?
Yes, you can use a 50L backpack for day hikes, though it is not ideal for most situations. The pack will work functionally—you simply will not fill it completely—but you will be carrying extra weight from the pack itself since larger packs have heavier frames, more padding, and additional features. This can add 1-2 pounds compared to a dedicated daypack before you even add gear. However, there are scenarios where a 50L pack makes sense for day hiking: if you are hiking in winter and need to carry bulky insulation layers, if you are bringing camera equipment or other specialized gear, or if you want one versatile pack that handles both day hikes and occasional overnight trips rather than owning separate packs. If you choose to use a larger pack for day hiking, use the compression straps to cinch it down and prevent the contents from shifting around, and avoid the temptation to fill empty space with items you do not really need.
How do I measure my torso for a backpack?
To measure your torso for a backpack, you need to find the distance between your C7 vertebra (the bony bump at the base of your neck) and the top of your hip bones. Start by tilting your head forward and running your fingers down the back of your neck until you feel a prominent bone that sticks out more than the others—that is your C7 vertebra and your starting point. Next, place your hands on your hips with your thumbs pointing backward and feel for the top of your hip bones (iliac crest). Mark this spot on your lower back. Have someone measure the distance between these two points using a soft measuring tape, keeping the tape straight along your spine. Most people fall into these ranges: 15 inches or less is extra-small, 15-17 inches is small, 17-19 inches is medium, and 19+ inches is large. Write this measurement down and bring it with you when shopping for packs, as it is far more important than your overall height. Many pack manufacturers list torso length ranges for each pack size in their specifications, and some packs offer adjustable torso lengths that can be customized to fit you perfectly.
What should I be able to fit in a 40L backpack?
A 40-liter backpack comfortably fits all the gear needed for overnight backpacking trips or very generous day hiking. For an overnight trip, you can fit a sleeping bag (compressed), a sleeping pad, a lightweight tent or hammock system, one change of clothes, a puffy jacket or fleece, a rain jacket, food for two days, a compact camp stove with fuel, a water filtration system or purification tablets, toiletries, a headlamp, and your first-aid kit. For day hiking, a 40L pack gives you substantial extra room for winter layers, photography equipment, or group gear like a shared tent or cooking system. The key to using a 40L pack effectively is packing organization—use stuff sacks or packing cubes to keep items compressed and organized, put heavy items like food and water close to your back and centered between your shoulder blades, and place frequently-needed items like snacks and your rain jacket in easily accessible pockets. Many hikers find 40L to be a versatile size that handles both robust day hikes and lightweight overnight trips, making it a popular choice for beginners who want one pack that can grow with their hiking ambitions.
The Bottom Line
Choosing the right pack size comes down to honestly assessing the type of hiking you will actually do, not the adventures you imagine you might do someday. If you are planning mostly short day hikes on maintained trails within a few hours of home, get a 25-liter daypack and save your money for other gear. For those with concrete plans to try overnight backpacking within the next few months, a 50-liter pack gives you room to learn what works without the bulk of expedition-sized options. And if you are already committed to multi-day trips or know you will be hiking in winter conditions requiring extra layers, a 60-65 liter pack provides the capacity you need without going overboard.
Remember that proper fit matters far more than having extra capacity. A 40-liter pack that fits your torso correctly and distributes weight to your hips will feel dramatically more comfortable than a 50-liter pack that does not fit, even if the larger pack has more features. Take the time to measure your torso length, try on packs with weight in them, and walk around for at least 15 minutes before deciding. The right pack should feel like it disappears on your back, letting you focus on the trail ahead rather than the gear you are carrying. Start with what matches your immediate plans, invest in proper fit, and you will have a pack that serves you well for years of hiking adventures.
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