Osprey backpack size depends mostly on the length of the torso. It is the main measure that decides the size of the bag. Many Osprey packs come in several sizes to fit various torso lengths.
To measure the torso at home, ask a friend to measure the back along the spine. Measure to the C7 vertebra, which is the knobby bone at the base when you tilt the head down. Based on torso length choose the best size
How to Choose the Right Osprey Backpack Size
Fit should not suffer because of other factors. Every person has a different body shape and needs a different size. Not every bag fits every person.
Adjustable models let you set the fit for the best carry feeling. Almost all Osprey packs have adjustable torso length, which really helps if you fall between two sizes.
Add a bit of weight to the bag before trying it. It does not matter if it does not weigh exactly as in real use for your activity, but being near to actual weight helps to judge the fit. Lift the pack from the knees.
Is it heavu? Then ask someone for help to wear it.
Osprey sizing is the same between models, so trying one can lead you to another. For instance, if you are between medium and large for the Atmos 65 AG, you could use any size, but the bigger one gives a bit more space. If you are on the limit between two, the small with a frame change also works well.
Sizing up or down is personal. Small packs are often narrow too, so broad shoulders do best with large, and narrow with small.
Osprey Xenith, Xena, Aether, Ariel, Atmos and Aura packs have interchangeable shoulder harnesses. That helps to set the comfort. Some models have sizes as small, medium, large and extra-large.
The running and biking vestpacks of Osprey use several sizes according to chest size, not torso.
To choose the right volume, a simple rule says: for a day trip an Osprey bag of around 15 liters is enough. Backpacking packs have 30 to 70+ liters. The Atmos AG 65 is good for multi-day backpacking.
Some models come in 50, 65 and 75 liters. Doubt about the rain cover? Take a bigger one, especially if gear is in outside pockets.
Buying in a store with a fit service is a wise notion. The retailer will measure along the spine until the C7 vertebra and will find the right size. Osprey cares that every outdoor lover finds the perfect fit, whether for a multi-day expedition or a fast day hike with a hydrationpack.
