Selecting the right backpack size for backpacking is essential for comfort, efficiency, and even your safety on the trail. This comprehensive guide covers every aspect related to backpack sizes, including measurement methods, usage scenarios, travel types, fit, packing, and advanced tips. Whether you’re planning your first overnight trek or strategizing for multi-week expeditions, you’ll find actionable advice to make the best choice.
Backpacking Backpack Size Calculator
Why Backpack Size Matters
The size of your backpack dictates what you can carry, how comfortable your journey will be, and whether you enjoy your adventure or suffer through it. A pack that's too small limits your essentials, while one too large tempts you to overpack, leading to unnecessary weight and discomfort.
How Backpack Sizes Are Measured
Backpack capacity is measured in liters (L)—the volume of all storage spaces, including the main compartment and extra pockets. This is the universal standard, regardless of brand.
- What you see labeled (ex: "50L") is the total volume of usable space.
- Some older packs are still listed in cubic inches, but liters are the modern standard. (1 liter ≈ 61 cubic inches.)
Backpack Size Chart: Length of Trip vs. Recommended Capacity
The most important factor is trip duration. Here’s a size breakdown based on trip length and style:
| Trip Length | Recommended Size | Comments |
|---|---|---|
| Half-Day Hike | 15–24L | Water, snacks, first aid, light jacket |
| Day Hike | 25–35L | Extra food, layers, more gear |
| 1–2 Nights | 35–50L | Overnight essentials, sleeping system |
| 3–5 Nights | 50–70L | More food, bulkier/warm clothes, tent |
| 5+ Nights/Exped. | 70–80+L | Extra fuel, food, winter kit, climbing |
- Ultralight packers can go lighter (smaller sizes) for longer trips if gear is highly compact and light.
- Family backpackers may need extra capacity for kids' gear on longer trips.
Backpack Size Categories Explained
15–30 Liters: Daypacks
- For day hikes and city exploration.
- Enough for snacks, water, small first aid kit, and an extra layer.
- Can double as carry-on for travel.
30–50 Liters: Overnight & Light Multi-Day
- Ideal for overnight treks, minimalist travelers, or short “fastpack” adventures.
- These sizes force packing discipline but keep your load light.
50–70 Liters: Standard Backpacking
- Workhorse sizes for 3–7 days in the wilderness.
- Accommodate a full tent, sleeping pad, bag, clothes, food, and extras.
- Most popular among regular backpackers.
70–80+ Liters: Extended/Expedition
- For long, unsupported trips, outfitting kids, or winter/cold-weather trekking.
- Best for those carrying heavy, specialized, or group gear.
How to Choose Your Ideal Backpack Size
1. Trip Duration & Style
- Will you be out for a day, a weekend, or weeks?
- Do you prefer comfort and extras, or are you an ultralight minimalist?
2. Equipment Bulk
- Bulky gear (like winter sleeping bags) needs more space.
- Ultralight kits with compressible gear fit in smaller packs.
3. Climate & Season
- Cold-weather and mountaineering require more clothing and insulation, increasing backpack volume needs.
4. Personal Packing Habits
- Are you a “just the essentials” packer, or do you like space for luxuries?
5. Body Size and Fit
- Your pack must match your torso length, not your overall height, for proper weight distribution and comfort.
- Most packs come in multiple sizes (S, M, L, sometimes XL).
Torso Measurement: The Foundation of Proper Fit
How to measure:
- Place your chin to chest and find the bony bump (C7 vertebra) at your neck base.
- Place your thumbs on the top of your hip bones (“iliac crest”).
- Have a friend measure the vertical distance from C7 to where a line between your thumbs meets your back.
Use this number to match the manufacturer's sizing for optimal fit.
Weighing Pack Weight vs. Size
- Don’t size up “just in case.” You’ll fill whatever space you have. Bigger often means heavier.
- Modern lightweight gear allows for smaller pack sizes for the same duration.
Other Key Fit & Comfort Considerations
- Hip Belt: Should comfortably transfer most weight to your hips.
- Shoulder Straps: Adjustable and padded for comfort. Avoid single-size fits all.
- Ventilation: Frames and mesh backs help reduce sweating on hot hikes.
- Compression Straps: Let you adjust the pack volume to stabilize partial loads.
Bag Features by Size
| Feature | Typical on Small Packs (≤30L) | Typical on Medium Packs (31–50L) | Large Packs (51L+) |
|---|---|---|---|
| Hydration sleeve | ✓ | ✓ | ✓ |
| Removable lid/floating top | — | Sometimes | ✓ |
| Sleeping bag compartment | — | Sometimes | ✓ |
| Internal frame | — | ✓ | ✓ |
| External gear loops | Sometimes | ✓ | ✓ |
| Adjustable torso | — | Sometimes | ✓ |
Packing Tips for Each Size
Small Packs (≤30L):
- Prioritize essentials; use stuff sacks to organize.
Medium Packs (31–50L):
- Use ultralight/compact gear; place heavier items near your back’s center.
Large Packs (51L+):
- Consider load distribution; don’t exceed 20–25% of your body weight.
Backpack Fit for Women and Youth
- Women’s-specific packs are tailored with smaller frame, contoured straps, and hip belts.
- Youth packs have adjustable torsos for growth and flexibility.
Common Backpack Size Mistakes
- Going Too Big: Leads to overpacking and back pain.
- Too Small: Forces you to leave critical gear behind.
- Ignoring Fit: A poorly fitting pack causes hot spots, soreness, and instability.
- Not Trying Loaded Packs: Always adjust and test packs with weight before committing.
FAQ: Advanced Backpack Sizing & Selection
Q: “Is a 40L backpack big enough for traveling?”
A: For many travelers and light packers, yes. If you use compression bags and pack ultralight gear, a 40L can suffice for multi-week journeys.
Q: Should I bring a 70L+ pack for a 2-week summer hike?
A: Only if carrying extra gear, for groups, or winter camping. Otherwise, 50–65L is sufficient for most summer multi-day trips.
Q: Do airlines allow large backpacks as carry-ons?
A: Generally, packs ≤45L meet most airline carry-on size restrictions, but always check specific airline policies.
The Verdict: How to Pick YOUR Ideal Backpack Size
- List all gear you intend to bring.
- Consider trip duration, climate, and packing style.
- Visit a store, try on several loaded packs, and walk around.
- Pick the smallest size that comfortably fits your gear.
- Ensure the fit matches your torso and is comfortable under load.
Final Packing & Buying Tips
- Try several brands, as fit varies by model.
- “Don’t buy too big just because you can—buy what you’ll carry.”
- Load your prospective pack to its expected weight before heading out.
By understanding backpack capacities, common use cases, and your own needs, you’ll find the perfect size for any backpacking adventure—optimizing comfort, safety, and trail enjoyment.