Osprey Atmos

Types of packs

Backpacking packs can be 30 to 70-plus liters. To choose the right capacity, consider trip duration and the gear you’ll bring.

Backpack features
Think about the frame type, location of important pockets, padding and ventilation, among other things.

Backpack fit
Your pack should be correctly sized for your torso length (not overall height) and hip circumference. A fit-expert at an REI store can help.

Consider your main activity:

• Hiking: Compatible with hydration reservoirs; some have straps or loops to attach trekking poles or other gear.
• Running: Designed to limit bounce; compatible with water bottles or hydration reservoirs.
• Climbing: Slim profile with abrasion-resistant reinforcements.
• Traveling: Has compartments for easy organization; many meet carry-on size requirements.

How much gear will you carry?

• 20L or less: Ideal for short runs, day hikes or quick outings.
• 21–35L: The sweet spot for hiking and travel.
• 36–50L: Best for extended trips or adventures requiring more gear or clothing.

Find the right fit:

• Daypacks are available in a range of sizes.

• Check your torso length and waist against the brand's size chart for the best fit.
• Many packs feature adjustable torso lengths to fine-tune your fit.

Choose a gear capacity 

• Runs under 2 hours: 2 liters 
• Runs 2-3 hours: 2 to 6 liters 
• Runs 3-6 hours: 4 to 12 liters 
• Runs over 6 hours: 6+ liters 

Decide on bottles and/or reservoir 

• Most vests are compatible with both bottles and reservoirs. 
• Bottles are easier and faster to refill, usually holding 500 ml of water each. 
• Bottles can be soft or rigid. Rigid bottles are more durable.  
• Reservoirs hold more water, up to several liters. 

Get the right fit 

• Follow the manufacturer’s sizing guidelines. 
• Choose a snug fit. (Measure your chest while wearing your sports bra.) 
• Leave room for adjustment: The straps should sit in the middle of their adjustment range. 
• Women-specific vests offer fits optimized for the bust and shoulders.