Step By Step Guide To Choosing The Right Backpack Size For Hiking

Selecting the right backpack is one of the most critical decisions a hiker can make. A poorly sized pack leads to discomfort, inefficient weight distribution, and even injury over long distances. Yet, many outdoor enthusiasts focus solely on brand or price, overlooking how volume, torso length, and load capacity affect performance. The ideal backpack isn’t about carrying more—it’s about carrying better. This guide breaks down the process into clear, actionable steps so you can match your pack to your adventure, body type, and gear list with confidence.

Understand Backpack Volume and What It Means

Backpack size is measured in liters, indicating the total internal volume. This number determines how much gear the pack can hold, but it doesn’t account for fit or comfort. Choosing the right volume depends primarily on the duration of your hike:

Trip Duration	Recommended Volume (Liters)	Typical Use Case
Day hike (under 12 hours)	15–30L	Water, snacks, layers, first aid, rain shell
Overnight or weekend trip	30–50L	Sleeping bag, pad, tent, food for 2–3 days
Multi-day trek (3–5 days)	50–65L	Full camping setup, extra clothing, cooking system
Extended expedition (7+ days)	65–85L+	Bulkier gear, resupplies, cold-weather equipment

It's tempting to oversize your pack “just in case,” but excess volume encourages overpacking. A well-filled 50L pack is far more efficient than an overstuffed 70L one. Stick to the minimum volume needed for your trip length and conditions.

Tip: If you're between sizes, choose the smaller pack. You'll be forced to pack lighter—a skill that improves efficiency and endurance.

Measure Your Torso Length for Proper Fit

A backpack that fits well distributes weight across your hips and shoulders, minimizing strain. The key measurement is torso length—not height. Two people of the same height can have vastly different torso lengths, which affects how a pack sits on the body.

To measure your torso length:

1. Stand naturally with feet shoulder-width apart.
2. Tilt your head forward slightly to locate the C7 vertebra—the bony bump at the base of your neck that protrudes when you bend forward.
3. Mark this spot with a piece of tape.
4. Locate the top of your hip bones (iliac crest). Find the natural curve where your pelvis meets your back; this is your iliac crest. Place another mark here.
5. Measure the vertical distance between the two points using a flexible measuring tape. This is your torso length.

Most packs are designed for specific torso ranges:

• Short: 14–16 inches (35–41 cm)
• Regular/Medium: 16–19 inches (41–48 cm)
• Long: 19–21+ inches (48–53+ cm)

Always check manufacturer sizing charts before purchasing. Some brands offer multiple frame sizes within the same model, while others only come in one size with adjustable harnesses.

“Fit is non-negotiable. A pack that rides too high or sags below your waist won’t transfer weight properly, leading to fatigue and discomfort.” — Daniel Reyes, Wilderness Gear Specialist, Appalachian Trail Conservancy

Match Capacity to Your Gear List

Volume recommendations are starting points. Your actual needs depend on what you carry. Ultralight backpackers often use smaller packs because their gear is compact and minimal. In contrast, families or winter campers may need larger volumes due to bulky items like insulated sleeping bags or bear canisters.

Before selecting a size, create a realistic gear list based on season, terrain, and personal habits. Then, simulate packing:

1. Lay out all essential gear.
2. Stuff items into a large trash compactor bag (which compresses similarly to a backpack).
3. Estimate volume: A standard 13-gallon kitchen trash bag holds ~50L. Compare how full your simulated pack becomes.

This method reveals whether you’re truly within a volume range—or if you’ll need to upgrade or downsize.

Real Example: Sarah’s Weekend Mistake

Sarah, an experienced day hiker, planned her first overnight trip in the Cascade Mountains. She borrowed a friend’s 75L mountaineering pack, assuming “bigger is safer.” On the trail, she struggled with excessive sway, poor ventilation, and constant readjustment. Her pack weighed only 18 lbs, but the oversized frame shifted unpredictably on steep descents. After consulting a gear specialist, she learned her torso was only 16 inches—better suited to a 50L women’s-specific pack. She rented a proper fit for her next trip and found immediate relief in stability and comfort.

Tip: Visit an outdoor retailer and try on loaded packs. Walk around, bend, squat, and simulate movement to test stability and pressure points.

Consider Frame Type and Load Support

The internal structure of a backpack influences how well it handles weight and adapts to your body. There are three main types:

• Internal Frame: Most common for hiking. Rigid stays and a flexible hip belt transfer weight to the hips. Best for rugged trails and loads over 20 lbs.
• External Frame: Traditional design with a visible metal or composite frame. Offers excellent ventilation and heavy-load support, but less stability on technical terrain.
• Frameless: Lightweight packs without structural support. Ideal for ultralight day hikes under 10 lbs. Not recommended for multi-day trips or heavy loads.

For trips lasting more than a day, an internal frame with a padded, load-lifting hip belt is essential. The hip belt should sit snugly on your iliac crest—not on your stomach—and carry 80–90% of the pack’s weight. Shoulder straps should complement, not bear, the load.

Do’s and Don’ts of Frame Selection

Do’s	Don’ts
Choose an internal frame for multi-day hikes	Use a frameless pack for heavy or extended trips
Ensure the hip belt locks securely over your hip bones	Let the shoulder straps carry most of the weight
Adjust the load lifter straps to pull the top of the pack closer to your shoulders	Ignore torso length just because the pack looks good
Test adjustability features in-store	Assume unisex packs fit all body types equally

“Many injuries stem from improper load distribution. A well-fitted internal frame reduces spinal compression and improves balance on uneven ground.” — Dr. Lena Patel, Sports Medicine Physician, Outdoor Health Institute

Step-by-Step Checklist: Choosing Your Hiking Backpack

Follow this sequence to ensure you select the right size and fit:

1. Determine trip length: Is it a day hike, weekend, or extended trek? Match to the recommended volume range.
2. Measure your torso: Use the C7 to iliac crest method to find your exact length.
3. List your gear: Account for season, water carriage, and cooking needs.
4. Simulate packing: Use a compactor bag to estimate required volume.
5. Try before you buy: Visit a store with fitting expertise. Wear hiking clothes and ask staff to help adjust the pack.
6. Load test: Add 15–20 lbs of weight and walk, squat, and twist to assess comfort and stability.
7. Check key contact points: Hip belt centered on iliac crest, shoulder straps snug but not pinching, sternum strap at collarbone level.
8. Evaluate accessibility: Can you reach the top compartment? Are hydration sleeves and side pockets functional?
9. Review return policy: Buy from retailers that allow field testing with a flexible return window.

Frequently Asked Questions

Can I use a 65L backpack for a day hike?

You can, but it’s inefficient. Larger packs lack targeted support for light loads and tend to bounce or shift. A dedicated daypack (20–30L) with fewer adjustment points is lighter and more agile for short trips.

What if my torso length falls between sizes?

Prioritize adjustability. Look for packs with sliding torso systems or modular harnesses. Some brands, like Osprey and Deuter, offer fine-tuned adjustments that bridge size gaps. Always test both sizes if possible.

Do women need different backpacks?

Yes. Women’s-specific models typically feature shorter torso lengths, narrower shoulder straps, wider hip belts (to accommodate pelvic structure), and lighter overall frames. While some unisex packs work, gender-specific designs often provide better fit and comfort.

Final Considerations: Weight vs. Durability

Once size and fit are confirmed, evaluate materials. Lightweight fabrics reduce pack weight but may sacrifice durability. For rocky terrain or bushwhacking, consider packs made with 210D or 420D nylon ripstop. Waterproof coatings or integrated rain covers add protection in wet climates.

Also consider access points: Top-loading packs maximize capacity but limit organization. Front-panel or zip-away access improves usability at the cost of added weight and potential failure points.

Tip: Balance weight savings with real-world demands. A 100g lighter pack isn’t worth it if it wears out after two seasons.

Conclusion: Pack Smart, Hike Better

Choosing the right backpack size isn’t about guessing or following trends—it’s a deliberate process rooted in anatomy, trip planning, and practical testing. By measuring your torso, matching volume to your itinerary, and prioritizing fit over features, you set the foundation for enjoyable, pain-free hiking. Remember, the best backpack disappears on your back: balanced, secure, and supportive. Take the time to get it right. Your body—and future adventures—will thank you.

💬 Have a backpack success story or fitting tip? Share your experience in the comments and help fellow hikers avoid common pitfalls.