Quick answer: Pick capacity by trip length, then fit by torso length and hip size, then features. REI suggests 30 to 50 liters for weekend trips, 50 to 80 for multiday and 70 or more for extended or winter trips. Torso length, not height, decides the size, and your hips should carry 80 percent or more of the weight.
Most bad backpack buys are fit problems, not brand problems. A pack that is the wrong torso length hurts no matter how good it is.
This guide follows REI buying advice in the order that matters.
Related: tent camping gear checklist, measuring your torso for a pack and how to pack a backpack.
Capacity by Trip
| Trip | REI capacity |
|---|---|
| Day hike | 10 to 40 liters, usually under 40 and about 30 lb or less |
| Weekend, 1 to 3 nights | 30 to 50 liters |
| Multiday, 3 to 5 nights | 50 to 80 liters |
| Extended, 5+ nights, or winter | 70 liters or larger |
Fit Comes Second
REI says torso length, not your height, matters most. Hipbelts typically fit hip sizes from the mid-20s to mid-40s inches, and some packs come in multiple sizes. Load lifters should form about a 45-degree angle with the shoulder straps. A hipbelt makes a noticeable difference once the load exceeds about 15 pounds.
Frame and Features
| Choice | Notes, per REI |
|---|---|
| Internal frame | Most common; transfers load to hips |
| External frame | Heavy or irregular loads; good ventilation |
| Frameless | Lightest; less comfortable with heavy loads |
| Features worth having | Sleeping bag compartment, tool loops, sternum strap, raincover, ventilated back panel |
Honest Limits
This is buying guidance, not a product review. We have not tested packs, and the right pack depends on your body and load. Try it on loaded.
Frequently Asked Questions
What size backpack for a weekend?
30 to 50 liters, per REI.
What size for a week?
70 liters or larger for 5+ nights.
Does my height decide pack size?
No. Torso length does.
How much weight should my hips carry?
80 percent or more, per REI.
Internal or external frame?
Internal for most; external for heavy, awkward loads.
Is a frameless pack good?
For light loads and fast hiking.
What angle for load lifters?
About 45 degrees.
Do I need a raincover?
It helps; waterproof stuff sacks are an alternative.
When does a hipbelt matter?
Once the load exceeds about 15 pounds.
Should I buy online?
Only if you know your torso length and can return it.
Bottom Line
Capacity by trip, fit by torso and hips, then features.
Load it and walk before you buy.
Sources: REI, How to Choose a Backpack; REI, How to Choose Daypacks; REI, Backpack Fit: Torso and Hip Size.