Let me guess—you’re standing in an outdoor gear shop or scrolling through page after page of backpacks online, wondering what the heck 18L or 65L actually means. More importantly, you’re trying to figure out which one is right for you without ending up with a bag that’s either way too tiny or totally overkill. We’ve all been there.
Choosing the right backpack size isn’t just about picking the coolest-looking pack or the one with the most pockets (though hey, pockets are great). It’s about matching the backpack to what you actually need to carry—and how you plan to carry it. So whether you’re prepping for your first day hike, packing for a weekend away, or gearing up for a month-long trek, this guide will help you sort through the clutter and zero in on the right size for your adventure.
First Off, What Does Backpack “L” Even Mean?
That little “L” you keep seeing? It stands for liters. It’s a measurement of capacity—not weight, and not dimensions, which is where a lot of people get tripped up. When a backpack says 25L, it means it can hold 25 liters’ worth of stuff in its main compartment and pockets combined.
Here’s a quick reality check: 25 liters of gear looks a lot different depending on how bulky your items are. A 25L pack full of clothes? Manageable. A 25L pack crammed with camera gear, a drone, and a tripod? Suddenly it’s tight.
Backpack Size Categories (With Real-Life Examples)
Let’s break this down by general size ranges and what they’re best used for. This’ll save you the pain of buying a 65L beast just to carry a water bottle and a sandwich.
6–10L: Ultra-Slim and Minimal
These are your tiny sling packs and hydration packs. Great for:
- Running or cycling
- Festival days when you just need water, sunscreen, and your phone
- Minimalist travelers who’ve unlocked some kind of packing sorcery
You won’t fit a jacket in one of these unless it’s paper-thin. And forget bringing your lunch.
11–20L: Daypacks for Essentials
This size is perfect for casual day hikes, short commutes, or sightseeing in a city. Think:
- Water bottle
- Snacks
- A light jacket
- A book or tablet
A 15L backpack is a sweet spot for everyday carry. Just don’t expect to fit a laptop and gym clothes in here too.
21–30L: Full Day Hike or Daily Commuter
This is the most versatile size range. Great for:
- Commuters who carry a laptop, charger, lunch, and maybe a sweater
- Day hikers bringing a first aid kit, camera, and lunch
- Travelers doing all-day excursions
You can usually squeeze in a change of clothes or two. Some people even manage to travel ultralight with a 28L pack, but they’re packing ninjas.
31–40L: Overnight or Minimalist Travel
You’re entering the overnight territory here. Packs this size are ideal for:
- Overnight camping trips in warm weather
- Travelers doing carry-on-only trips (hello, airline cabin size limits!)
- Students carrying books, a laptop, and gym gear
You’ll start to notice more serious support systems—hip belts, chest straps, and better padding—because these can get heavy when fully loaded.
41–55L: Weekend Trips and Travel Backpacks
This is your weekend warrior sweet spot. Enough room for:
- Clothes for 2–4 days
- Toiletries, electronics, and maybe even a pair of shoes
- Light camping setups if you’re going minimalist
This is also the size range where you start needing to think about load distribution—how the pack handles when it’s full. Make sure the shoulder straps and back panel are actually comfortable.
56–70L: Extended Travel or Multi-Day Treks
Planning a multi-day hike? Backpacking across Southeast Asia for a month? This is your zone. You’ll be able to carry:
- A tent, sleeping bag, and cooking gear
- Clothes for a week or more
- Food and water for a couple days
But let me be honest—if you’re packing 60L worth of gear, it’s going to be heavy. Don’t buy this size unless you actually need the space. Otherwise, you’re just lugging around dead weight.
70L+: Expedition or Max-Volume Travel
This is “big adventure” territory. Think:
- Long mountaineering expeditions
- Harsh winter camping where bulkier gear is required
- Extended off-grid travel
Some travel backpacks also sneak into this size if they have expandable compartments. But for most people, this is way more than you need unless you’re going into the backcountry for weeks.
Don’t Just Look at Liters—Think About These Too
The liter rating is helpful, sure. But there’s more to backpack size than just the number.
1. How It’s Packed: A 40L top-loader with one big compartment will feel very different from a 40L clamshell-opening travel bag with compression panels.
2. Frame or No Frame: Some packs come with internal frames, especially from 35L and up. That adds weight, but also comfort for long hauls.
3. Torso Length Matters: Especially on hiking packs. Many come in different torso sizes or offer adjustable harness systems. A good fit here makes or breaks your experience.
4. Pockets and Compartments: Are you the kind of person who likes a place for everything? Some 30L packs feel roomier than 40L ones just because they’re smarter about organization.
5. The Shape of the Pack: Slim and tall? Short and fat? Long torso? Barrel chest? Yeah, how the bag fits on your body matters too.
What Size Backpack Do You Need?
Here’s the part that actually helps you decide.
For Travel:
- Weekend trip (2–3 days): 30–40L
- One-week trip (carry-on only): 40–45L
- Multi-week backpacking (hostels, trains, etc.): 45–60L
- Living out of your pack (nomadic): 55–70L, but only if you can handle it
For Hiking:
- Short hikes (1–4 hours): 15–25L
- Day hikes with lunch and layers: 20–30L
- Overnight hikes: 35–50L depending on gear
- Multi-day treks: 50–70L with proper support
For Commuting or Daily Use:
- Laptop, lunch, and essentials: 20–30L
- Gym + work setup: 25–35L
- Student life with books and tech: 25–40L, padded laptop sleeve is key
For Adventure Sports:
- Cycling or trail running: 6–15L
- Ski touring or alpine missions: 20–35L
- Climbing (gear-heavy): 30–50L, depending on rope size and harness load
One Last Thing: Don’t Oversize Just Because
It’s super tempting to go bigger “just in case,” but that’s a fast track to overpacking. You will fill whatever space you have. Every extra liter invites one more pair of socks you don’t need.
Pick the smallest size that fits your actual needs. Your back, shoulders, and future self will thank you.
If you’re unsure, go try on a few different sizes in-store with actual weight inside. The feel of a 35L pack with 8kg inside is wildly different from trying it on empty.
Final Thoughts
The right backpack size is about more than numbers—it’s about the trip you’re taking, your body, your gear, and how you move through the world. You don’t need a spreadsheet to figure it out, just a little bit of honesty with yourself.
What are you really going to use this for? What do you actually need to carry? And how much are you willing to haul around day after day?
Once you’ve answered those questions, that mystery 28L or 50L tag isn’t quite so cryptic anymore. It becomes the key to a bag that fits your life perfectly.
And if you nail it? You’ll barely notice the bag at all—which is exactly how it should be.
