I'm trying to decide on daysack for light hiking (no mountains, clement weather). There's plenty of guides online, but I can't seem to make sense of them.

This one, for example says

20-30 Liters

Most daypacks fall under this category. These are made to include the essentials such as food for the day, light insulation layers (puffy or fleece jacket), rain shell, a headlamp, a small first aid kit, and a space blanket.


30-40 Liters

This is the category where most weekend and overnight backpacks fall under.

These backpacks could fit everything you’d need for a 2 or 3-day adventure, including a lightweight sleeping bag, food for up to 6 meals, hammock/lightweight tarp/ultralight one-person tent, small sleeping pad, underwear, and an extra pair of socks.

There are loads of similar examples on hiking websites and YouTube.

I've measured my stuff (plus some official measurements from the websites of stuff I haven't bought yet (I'm new to this)

  • Tent - 6l

  • Sleeping bag -8l (compressed)

  • Bedmat - 2l

  • 2l extra water

  • 1l extra food

  • 4l spare clothing

  • 1l cooking pot

(I also measured all my day hike stuff using the DoE kit list - It comes to 15l)

That's 24l bare minimum for my overnight additions. So I can't see how whatever pack I get for camping, my daysack isn't going to want to be at least 24l less.

Yet every website and video I seem to find has a difference of less than half that (10l in the example above). Even the ultra lightweight stuff doesn't seem to gain much in volume (just weight).

So my question is basically what are people carrying in a daysack that needs 20-30l, and how are they adding only 10l to that to turn it into an overnight camping bag?

  • I personally carry a fully stocked first-aid kit in my day-pack with sam splint, extra expired epis, and other specialty things, because I'm more concerned having to help other groups (check your local regulations on what you can and can't do as far as treatment goes). That takes 1/3 of my 32L day pack. I don't carry that in my overnights because it takes too much room, so there's actually a larger volume gain that 13L from my day pack to my overnight pack even though it's a 45L pack.
    – Gabriel
    Commented Jun 10, 2021 at 20:14
  • @Gabriel - regarding your epi(pens) - if they are anything more than 6 mo expired, they aren't worth the weight. Apparently (according to medical literature) there's quite a bit of evidence that they don't keep well at all, and may not be fully functional even earlier than the time of expiry.
    – bob1
    Commented Jun 10, 2021 at 20:33
  • @bob1 I am aware, but I have a relatively reliable stream of expired from a first responder family member. The idea is that reduced efficacy is always better than nothing if you encounter grave reactions. Anyway, in several places I wouldn't even give epi to someone else, I might get in trouble.
    – Gabriel
    Commented Jun 10, 2021 at 20:41
  • @Gabriel - good to know that you are aware. I agree with the something is better than nothing approach here - just you might have to give several to see any effect.
    – bob1
    Commented Jun 10, 2021 at 22:23
  • 2
    IMO 30-40l is really too small for overnight backpacking, unless you go for ultralight everything, which your quote hints at. My 40l is my winter daypack (sadly used more for shopping at the moment
    – Chris H
    Commented Jun 11, 2021 at 11:26

4 Answers 4


First of all, you may be able to get 1 1/2 buckets of water into a 15 l backpack (and I wouldn't even be too sure about that because they may have rounded, and the measurements may be the outside measurements), but that doesn't mean that you'll get your sleeping bag compressed to 8 l next to the 6 l tent inside said 15 l pack. Not to speak of the "bump" an airing system for your back causes - that may make a quite awkward shape for the compartment.

Much easier to strap down (= flat) a larger backpack which allows you to arrange stuff nicely close to your back.

For day/single night outings I use a 45 - 55 l bag. I have a big one for longer/winter tours in addition, but no smaller one in regular use. Mostly because I like the back (and proper hip belt) of 50 l bag so much better that I consider it worth while carrying that bag even if it is almost empty.

Also, with some good friends I've found it a nice strategy to use one such backpack for two people and change whose back is wet every once in a while.

When is that bag "full"? In winter/cold-wet or unstable weather, when I have additional photo equipment (my tele lens alone is bigger than @Gabriel's tent...), when I bring the laptop as well because I combine work with a hike, when I use it for shopping. In contrast to @BenCrowell, I often carry (initially) substantially more than 2 l of water (in hot weather, I'm easily in the range of 1 l/h).
Also I use one of those old-fashioned foam pads that take up a lot of volume in exchange for being basically indestructible and lighter than most of the inflatble ones. Also the rest of my equipment is not volume optimized at all, most of it 3 or 4 seasons. Even though I could do perfectly well without stove for many multi-day tours (say, 3 seasons), I may consider the luxury of having hot coffee worth bringing my stove for just one night... And that's a gasoline one. (I'm in Germany, lighting a wood fire in a forest is basically a BIG no-no over here)

Iow: as long the bulk or weight doesn't disturb you, it's fine to bring it. For an alpine tour with lots of elevation, I think harder about what exactly to bring (but then, many of these things become a safety consideration and you bring them anyways).


I tend to buy big, then use the side compression straps to shrink it to that the load covers my back. This allows me to take a fairly complete camera kit as well as a sleeping bag and emergency tarp, spare clothing for a winter day trip that may turn into a winter overnight.

I don't like little packs without a waist belt. I want a pack that goes from my hip bones to my shoulders at minimum. Smaller ones tend to either be useless for anything more than a windbreaker and a roll of toilet paper, or dig into shoulders and small of my back, and flop all over in rough terrain.

For longer trips I use an external frame Greggory (no longer made) that has a fairly modest main compartment, but has a shelf on the bottom and on the top. Food goes in a sleeping bag stuff sack on top, sleeping bag and foam pad and tarp go on the bottom. Tripod is fastene with ladderlock straps to the side frame.

  • I also use larger bags with side compression. They work very well (and mine are 90s/early 2000s Karrimor). The exception, oddly enough, is when I'm hiking with my SLR gear. For that I use a LowePro cabin-luggage size backpack with multiple compartments and good padding (still with the tripod on the outside)
    – Chris H
    Commented Jun 17, 2021 at 11:34
  • I don't like little packs without a waist belt. I want a pack that goes from my hip bones Surely that means you want a hip belt and not a waist belt - or is this distinction not used everywhere? (I think that quote, the clearest I could find, is from someone also in the UK)
    – Chris H
    Commented Jun 18, 2021 at 15:44

If you're going to buy small backpack, like 20-30 liters, do not overthink and take simple model without much extras like the internal metal frame. Cheap simple backpack will work better because it's easier to bend and hide under your seat while commuting etc. It's just an universal backpack that you take for short hikes, small groceries or commuting.

A bigger backpack will also be your friend. It would work fine for bigger groceries, short trips with sleeping over in hotel, or backpacking with an ultra light tent.

A bigger backpack (70 liters or more) would be perfect for longer trips, like vacation.

So unless you're extremely tight on budget, owning at least 3 sizes of backpacks is certainly a good invested money. They are not only for outdoors, but replace a purse or suitcase in the everyday life.

The question how big backpack you need for a trip is practically unanswerable. This depends on so many factors. Having 3 backpacks you just start packing, and if it's not enough, you decide between taking bigger backpack or reducing your stuff. Some people go really extreme, eg. taking only 2 pairs of socks, even for a 2 week hike. Guess they sit alone even in an overcrowded train ^^ ...

  • The 2 pairs of socks thing is not as bad as you depict it... I use one pair for hiking, and another for sleeping and "civilization". (Admittedly, I don't tend to get smelly feet, though.) Commented Jun 13, 2021 at 9:05

Welcome to outdoors.SE!

The day packs I own are 16, 23 and 30 liters. The overnight backpacking packs I own are 66, 70, and 75 liters. However, all of the large ones have features that allow their volume to be shrunk quite a bit, and I'm often not using the whole volume. You can shrink their volume using compression straps or by not extending the top of the pack up to its full height.

How much volume you'll need depends on a lot of different factors and choices. Do you keep your sleeping pad inside or outside the pack? Are you in an area where bear canisters are required?

On your list, a lot of items seem pretty bulky. I would not carry 4 l of spare clothes. The tent and sleeping bag sound big and bulky. One of the things you're paying for in an expensive down bag is the ability to pack it down very small. Ultralight tents are much, much smaller than what you're describing.

If you're going to a dry area like California, then I'd question whether you need the gigantic bulky tent. You could just bring a tarp in case it rains.

If you're going to a wet area like England, then I'd question why you'd ever need to carry 2 liters of water on your back. Even here in California, I seldom need to carry that much.

  • That's also my take. My tent is 2L, sleeping mat is 1L, sleeping bag + night clothes 3L. Right there it's a huge difference.
    – Gabriel
    Commented Jun 10, 2021 at 20:20
  • This is all really useful, thanks. One thing I'm still unclear on though is - wouldn't the ultra-lightweight ethos apply to the daypack too? If you've an ultra small overnight kit, you'd have an ultra small day kit too? So your daysack would still be a lot smaller than your overnight pack (as yours are, it seems - ~50L differences, way more than the 10L or so I'm finding suggested online). I still don't really understand where this 20-30L idea comes from. The problem I still have is that I can't even (theoretically) fill a 23L daysack let alone 30L. Commented Jun 11, 2021 at 6:51
  • 1
    @Gabriel - Wow! 2L tent and 3L sleeping bag, that's really small. Can you say what make/model they are? I doubt I could afford such technical gear, but I'd love to have a look. Commented Jun 11, 2021 at 6:53
  • I'm in England, and unless you're up in the mountains above farm level, almost any water you can find will probably be polluted. You even have to be careful with springs Filters/chlorine tablets will deal with the biological contamination, but n many areas popular for hiking you get fertiliser run-off and the like. OTOH we're quite densely populated and refilling isn't too hard. I'll be taking 2l of water road cycling tomorrow; I drink a lot, but know I can refill a couple of times
    – Chris H
    Commented Jun 11, 2021 at 11:31
  • @IsaacBraham: One thing I'm still unclear on though is - wouldn't the ultra-lightweight ethos apply to the daypack too? Not really, in my experience. The problem I still have is that I can't even (theoretically) fill a 23L daysack let alone 30L. In warm weather, I would use my 16 l pack. I would switch to the 23 or 30 l packs if it's winter and I need a lot of layers of clothing plus possible extras like crampons and helmet, or snowshoes if they're needed and I want to fit them inside. Similar idea for rain gear.
    – user2169
    Commented Jun 11, 2021 at 14:23

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