What size pack for overnight backpacking?

What size pack would everyone recommend for an overnight backpacking trip? I'm curious about different scenarios for one person, two and four people, ranging from 5, 10, and 20 mile round trip hikes.

Personal experiences?

Most of my backpacking is going to be near Las Vegas at Mt. Charleston and Red Rock Canyon. Possibly out in the grand canyon if we get some 3 day weekends soon.

Thanks!

I use a 3800 cu. in "Deluxe" from Mystery Ranch and it is ideal. I can pack everything inside except the extra foamy that I like to use with a TR PL4 and can go for 2 nights-3 days, easily, in warm weather, of course.

how big of a tent and sleeping bag do you carry?

I usually just use an Integral Designs Unishelter for such trips in summer.

My bag for these trips is a Western Mountaineering Alpinlite Super.

So, my gear for 1-2 night May-Sept. trips is pretty compact and light. If, I "need" a tent, my Hilleberg Soulo would go along and it is pretty compact, as well.

Another option I am considering is to buy an ID bugtent and pair it with the ID Siltarp III, that I already own, this will probably happen next year and is also a compact setup.

so a 1800cu. in. pack would be more of a day hike kind of deal? I guess it would be possible to do some over nights, but I should probably just go with at least a 3800cu. in. pack just so i can have that diversity in case i want to go out for a few nights.

If you are going up Mt. Charleston I'd take some cooler weather clothes with you. Its a long climb/walk up the mountain, and I want to say its about a 3,000 foot elevation change.

Red Rock is a different story... I'd hike naked there if I could. And with a portable fan. Err. Make that industrial fan. You will come out looking like a lobster.

1800cu. in. is basically a slightly-enlarged book bag. Chances are it won't have any suspension for carrying a heavy load. So yes, 1800cu. in. is really more around day pack size.

For an over-nighter, you're going to need to bump up to at least 35L (appx 2100 cu. in.). I have an Osprey pack that tows in at 45L (appx 2750 cu. in.) and that has proved the perfect size for most 2-3 day adventures, and longer if you are group trekking with a few others.

If you are thinking about working up to weekenders (2-3). Then I would target something at least 40L and probably not bigger than 50L.