The right backpacking backpack size is 45–50 liters for 1–2 nights, 50–70L for 3–7 nights, and 70+L for week-long trips or winter expeditions, matched to your torso length, not your height.
One wrong size turns a great trail into a painful one. Too small, and your gear won’t fit. Too large, and you carry dead weight that wobbles on every step. The fix is simple: match the liter capacity to your trip length and your torso measurement to the pack’s adjustment range. This guide walks through both numbers, tells you which volume fits common trip types, and explains how to measure yourself so the pack lands right on your hips.
Trip Length Determines Pack Volume
How many liters you need depends almost entirely on how many days you’re carrying gear and food. A 1-night summer trip and a 7-night shoulder-season trek need dramatically different space.
The table below lays out the standard volume guidelines by trip type, drawn from gear manufacturers and outdoor organizations:
| Trip Duration | Recommended Volume | Use Case Notes |
|---|---|---|
| Day hike (summer) | 15–20L | Fast-and-light, minimal gear |
| Day hike (cold/photography) | 25L | Extra layers, camera equipment |
| Weekend (1–3 nights, ultralight) | 30–35L | Silnylon tarp, down quilt, alcohol stove |
| Standard 1–2 nights | 45–50L | Fits a bear canister, 3-season setup |
| 3–7 nights | 50–70L | Food volume is the limiting factor; 60L is the ideal middle ground |
| 7+ nights or winter | 70–90L | Holds 50–60 lb loads, extra insulation |
| Expedition or thru-hike | 65L+ | 65–75L in winter; 50–55L for an ultralight thru-hike |
A key rule from Eiken Shop: pack your gear first, weigh it, then choose a pack that offers about 10% extra volume over your total gear volume. That’s enough wiggle room without encouraging overpacking.
How To Measure Your Torso Length For A Pack
Height tells you almost nothing about which pack size you need. Two people of the same height can have completely different torso lengths and need different packs. The measurement is straightforward.
You’ll need a flexible tape measure and a helper. The American Mountaineering Center (AMC) describes the method:
- Find your top point — the seventh cervical vertebra (C7), the bony bump at the base of your neck where your neck meets your shoulders.
- Find your bottom point — rest your hands on your hips with fingers forward and thumbs back. The imaginary line between your thumbs sits at the top of your iliac crests (hip bones). The center of that line is your bottom point.
- Measure the span between C7 and the iliac crest line, in inches or centimeters.
- Check the manufacturer’s torso chart for that specific pack model. Many packs now offer adjustable torso lengths with locking mechanisms, giving you more room to dial in the fit.
Most packs accommodate a torso range starting at 38–42 cm, according to AMC Outdoors. If you land between sizes on a fixed-length pack, size up.
Why Hip Belt Fit Matters More Than Shoulder Straps
The hip belt carries 75–80% of the pack’s weight when properly fitted. The shoulders and sternum strap only stabilize the load; they aren’t meant to bear it. Measure your hip circumference at the top of your hip crests — the same level as the iliac crest line. Wear the clothing you’ll hike in (shorts plus a fleece plus a rain shell, for example) to get an accurate measurement.
A pack with a thick padded hip belt and a frame becomes essential when your base weight exceeds 10 pounds. Without a frame, weight transfers straight to your shoulders, causing discomfort within a few miles.
What About Airline Carry-On Limits?
If you’re planning a trip that mixes backpacking with air travel, pack volume faces a hard ceiling. US airlines allow a carry-on up to roughly 22 by 14 by 9 inches, which caps volume at about 45 liters. Budget and international airlines often limit you to 35–40 liters for overhead bins, and personal items (under the seat) max out around 18 by 14 by 8 inches.
That 45-liter maximum is perfect for a 1–2 night trip but won’t cover a 5-night trek. For longer trips you’d check the bag, so buy a pack that fits the trail first and plan your baggage strategy second.
The 10% Headroom Rule And Common Sizing Mistakes
Most beginners add 30% headroom when picking a pack size, assuming “extra space is better.” That extra volume encourages packing extra items and kills the pack’s stability. The rule from gear experts is cleaner: select a pack that fits your gear with about 10% room to spare.
Other mistakes to avoid:
- Choosing by height instead of torso length — this is the single most common error, and it causes poor hip-belt fit and shoulder strain.
- Ignoring food volume — three or more days of trail food adds significant bulk. That’s why the 50–70 liter range exists; the food takes up real space.
- Assuming 45L fits every airline — budget carriers often require 35–40 liters max. Check your airline before you commit.
- Buying the pack before buying your other gear — lay out your shelter, sleep system, cook kit, food, and water, then find a pack that holds the total. Buying the pack first forces you to cram your gear into whatever volume you chose.
Once you know your volume range and torso measurement, try on a few models from reputable outfitters. If you’re shopping online, make sure the retailer accepts returns for fit issues — the best spec on paper means nothing if the pack doesn’t fit your body.
For readers who also need a solid everyday option for travel or commuting, our roundup of the best city backpacks for daily use covers tested picks for a different kind of carry.
Torso Measurement Quick Reference
Here’s a compact summary of the fit landmarks and their roles:
| Measurement | How To Find It | Why It Matters |
|---|---|---|
| Torso length | C7 vertebra to iliac crest line | Selects pack size and frame height |
| Hip circumference | 360° at top of hip crests | Hip belt carries 75–80% of weight |
| Comfort weight limit | Manufacturer’s spec (often ~25 lbs) | Exceeding it means discomfort on the trail |
| Base weight threshold | Over 10 lbs needs a framed pack | Frameless packs fail above this limit |
If your fully loaded pack exceeds that range, lighten your gear before you upgrade the pack.
FAQs
FAQs
Can I use a 40-liter pack for a 3-night trip?
Yes, if you own ultralight gear — a down quilt, a tarp-style shelter, minimal cook system, and compact food — a 40-liter pack can handle three nights. But if your sleeping bag is a synthetic mummy and your tent packs large, a 50-liter or larger pack will be more comfortable.
What size backpack do I need for a thru-hike?
Thru-hikers on warm-weather trails like the Pacific Crest Trail often use 50–55 liter packs, especially if they go ultralight. Winter thru-hikes or trips through very remote sections push that up to 65–75 liters to handle extra food and insulation.
Is a 70-liter pack too big for a weekend trip?
Yes, in most cases. A 70-liter pack encourages overpacking and carries unnecessary weight for a 2–3 night outing. Reserve 70+ liter packs for trips of 7 days or longer, or winter conditions requiring bulky cold-weather gear and extra food.
Do I need a framed or frameless pack?
If your base weight (everything except food and water) exceeds 10 pounds, choose a framed pack with a padded hip belt. Frameless packs work for ultralight setups under 10 pounds but transfer weight directly to your shoulders, causing fatigue on longer days.
How do I know if my pack fits before a trip?
Load the pack with your estimated trip weight, adjust the hip belt so it sits on your iliac crests, then tighten the shoulder straps until they touch your shoulders without lifting the weight off your hips. Walk around for 20 minutes. If the pack shifts, pulls at your shoulders, or rubs your neck, the fit is wrong.
References & Sources
- Eiken Shop. “What Hiking Backpack Size?” Volume recommendations by trip length and the 10% headroom rule.
- AMC Outdoors. “How to Choose the Right Backpacking Pack.” Official torso and hip measurement protocols.
- REI. “How to Choose a Backpack: Sizing & Fit Guide.” Detailed sizing advice and pack selection criteria.
- Travelpro. “What Size Travel Backpack Do You Need?” Airline carry-on dimension limits for pack volume.
- Gossamer Gear. “What Size Backpack Do I Need for Backpacking?” Ultralight pack volume recommendations and bear canister clearance.
Mo Maruf
I created WellFizz to bridge the gap between vague wellness advice and actionable solutions. My mission is simple: to decode the research and give you practical tools you can actually use.
Beyond the data, I am a passionate traveler. I believe that stepping away from the screen to explore new environments is essential for mental clarity and physical vitality.