What Size Backpack Do I Need for an Overnight Hike?

https://mountainsforeverybody.com/what-size-backpack-do-i-need-for-an-overnight-hike
In the case of an overnight hike you will likely carry a tent, a sleeping pad, and a sleeping bag. The size of your pack will therefore mainly depend on how bulky these three items are. This will be determined by the season and climate, and by how much you want to spend on your equipment.

If your pack has the usual attachment options so that you can carry at least some of the bulky items attached from outside, then you can think about a pack with the volume of 40-50 liters. This will be large enough for everything you need for an overnight hiking adventure.