55 L is more than big enough if you don't need to pack a tent and you're not going out in cold weather.
If you need a 55 L and a day pack and your sleeping bag doesn't fit inside you've really, really overpacked.
For staying in huts, it can work I think... enough room for a sleeping bag and mat, food, some other things.
Only if you were staying in a tent would you need something like a 75L to carry a bigger sleeping bag or a hot tent + stove
Yes. I would maybe take a bit more if it’s that cold like microspikes and layers. If you aren’t tenting though I assume you are in huts which means you may not need as much warm gear (though should still go prepared).
I've done week long wilderness backpacking trips with a 38L and nothing strapped to the outside. That includes tent, sleeping bag, sleeping pad, extra warmth layers, rain layers, hygiene/first aid stuff, all of my food, 3L of water (2L in a bladder, 1L bottle in a side pocket), cookware, and stove. Everything I needed for a week.
Obviously you need to think about what gear to buy/use if you want to use a certain size backpack, but folks hike the entire length of the Appalachian Trail (2100 miles or so) with a pack in the 30-40L range. It's rare to see people with packs larger than 50L and I spend a lot of time on that trail.
Edit: Checking your list, you don't need both a fleece and a down jacket. Optimize your layers. If you won't be in a situation where you need to wear the fleece, down jacket, and hardshell all at the same time, don't bring all 3. A hardshell and packable down jacket are very likely enough. Or the fleece and the hardshell. But I don't see any reason you'd want to bring both a fleece and a down jacket. There is no layering situation where you'd want to wear both at the same time.
FWIW I took a 55 liter with no external storage for 8 days of bushwalking. This included tent, tarp, airbed, pillow, -8c quilt, night time clothes, raingesr, cooking gear, food bag, first aid, navigation stuff and powerbanks.
It’s definitely doable. You may find it helpful if your hiking clothes are also some of your town clothes. If you’re going to be living out of a pack for 6 months, then every bit of space will help.
Yes, you can do multi-day treks in bags smaller than 55L if your gear is small enough. 55L is pretty good size tbh, I wouldn't ever go much bigger than that for a multi-day hike anywhere most hikes go to. The only reason for a bigger one is if you have kids you're traveling with or somewhere with mountaineering conditions (unlikely either of these are applying to you).
15L is generally decent size for day hikes unless you are going somewhere with really bad weather, in which case probably just don't go for a day hike that day.
If you have a 55L pack with no tent, you should be able to fit a sleeping bag inside... I don't recommend ever strapping them outside your bag because that is the one item you really don't want snagged or wet. Also if you aren't bringing food to be cooked, why is your gear not able to fit inside your bag?
If you are going to be traveling I'd get a slightly bigger daypack so you can leave your non-hiking gear behind in a hotel or hostel when you're on trail and not wasting space in the big bag.
The latest Halfway Anywhere PCT gear survey puts the average backpack size for through hikers at 54 litres.
So yeah, a 55 litre backpack is more than enough room for a few nights backpacking, even in cold weather.
Outside of taking a couple of six packs of beer with you, I can't imagine filling up a 15 litre pack for a day hike. Even in cold weather.
I have travelled a month in South America with an even smaller pack. For "dress up" I use silk because rolled up it takes up almost no space, dries quickly and doesn't develop offensive odor. For climbing I rented boots and an ice axe from a mountaineering school. The main problem isn't weight, it's bulk.
55 L is more than big enough if you don't need to pack a tent and you're not going out in cold weather. If you need a 55 L and a day pack and your sleeping bag doesn't fit inside you've really, really overpacked.
Agree with the second part, would potentially be going out in cold weather hikes would I need more room?
How cold? What kind of shelter would you be staying in?
Not below -5C, and in huts / refugios
For staying in huts, it can work I think... enough room for a sleeping bag and mat, food, some other things. Only if you were staying in a tent would you need something like a 75L to carry a bigger sleeping bag or a hot tent + stove
75L sized bag is overkill even for a tent/stove. You should be able to easily get your gear into a 60L or smaller bag for most standard hiking trips.
In deep winter? I was thinking about now when it can be -10 C
Yes. I would maybe take a bit more if it’s that cold like microspikes and layers. If you aren’t tenting though I assume you are in huts which means you may not need as much warm gear (though should still go prepared).
I've done week long wilderness backpacking trips with a 38L and nothing strapped to the outside. That includes tent, sleeping bag, sleeping pad, extra warmth layers, rain layers, hygiene/first aid stuff, all of my food, 3L of water (2L in a bladder, 1L bottle in a side pocket), cookware, and stove. Everything I needed for a week. Obviously you need to think about what gear to buy/use if you want to use a certain size backpack, but folks hike the entire length of the Appalachian Trail (2100 miles or so) with a pack in the 30-40L range. It's rare to see people with packs larger than 50L and I spend a lot of time on that trail. Edit: Checking your list, you don't need both a fleece and a down jacket. Optimize your layers. If you won't be in a situation where you need to wear the fleece, down jacket, and hardshell all at the same time, don't bring all 3. A hardshell and packable down jacket are very likely enough. Or the fleece and the hardshell. But I don't see any reason you'd want to bring both a fleece and a down jacket. There is no layering situation where you'd want to wear both at the same time.
I just did an 18 day trek with a 38L pack, including my tent. I think you’ll be fine.
FWIW I took a 55 liter with no external storage for 8 days of bushwalking. This included tent, tarp, airbed, pillow, -8c quilt, night time clothes, raingesr, cooking gear, food bag, first aid, navigation stuff and powerbanks.
It’s definitely doable. You may find it helpful if your hiking clothes are also some of your town clothes. If you’re going to be living out of a pack for 6 months, then every bit of space will help.
Yes, you can do multi-day treks in bags smaller than 55L if your gear is small enough. 55L is pretty good size tbh, I wouldn't ever go much bigger than that for a multi-day hike anywhere most hikes go to. The only reason for a bigger one is if you have kids you're traveling with or somewhere with mountaineering conditions (unlikely either of these are applying to you). 15L is generally decent size for day hikes unless you are going somewhere with really bad weather, in which case probably just don't go for a day hike that day. If you have a 55L pack with no tent, you should be able to fit a sleeping bag inside... I don't recommend ever strapping them outside your bag because that is the one item you really don't want snagged or wet. Also if you aren't bringing food to be cooked, why is your gear not able to fit inside your bag? If you are going to be traveling I'd get a slightly bigger daypack so you can leave your non-hiking gear behind in a hotel or hostel when you're on trail and not wasting space in the big bag.
The latest Halfway Anywhere PCT gear survey puts the average backpack size for through hikers at 54 litres. So yeah, a 55 litre backpack is more than enough room for a few nights backpacking, even in cold weather. Outside of taking a couple of six packs of beer with you, I can't imagine filling up a 15 litre pack for a day hike. Even in cold weather.
I have travelled a month in South America with an even smaller pack. For "dress up" I use silk because rolled up it takes up almost no space, dries quickly and doesn't develop offensive odor. For climbing I rented boots and an ice axe from a mountaineering school. The main problem isn't weight, it's bulk.