30L Backpack

No. Assuming you pack light.

Sounds a bit small to me. Not that you need a bigger pack for a one month trip than you do for a one week trip, but my main pack (which I've used for trips up to ten months) is 45L, and it's usually fairly full. Of course, if I cut back on books and electronics and footwear, I could get by with something smaller.

Only you can determine that. Create a packing list of essentials and clothing. Get the backpack, pack everything from your list in that pack and see if it fits. If it doesn't, either remove items or get yourself a larger pack. You are really packing for one week, but traveling for 4. The season of travel will also determine the size of the pack. If you are traveling in cooler temps, or colder countries, you will need a bit more clothing for layers. you can wear just one outfit, and bring just one more, take one pair of shoes (the ones you wear). Guys can get by usually without anything but a razor. My husband just uses the shampoo at the hotel, but brings deodorant. Based on your 'wants' you may require some space in the bag to bring back items you purchase, perhaps a gift for a friend? Make sure you either have a small second duffel or room in the pack for "extras' you pick up along the way. (or not - if you are the type to just want the experience and don't need the material items some people have to have when they travel)

Alex, Some of the die-hard "minimalist travellers" can manage just fine with a 30 L. Backpack, but I'd find that capacity far too limited. The size of Backpack is very much dependent on one's travel style and preferences, so only you can decide if that will be adequate for the kit you want to travel with. Cheers!

30L is about 1830 cu in (1L=61.02 cu. in.), not 1200. I think 1200 cu. in. would be a little small, but 1800 would be big enough for me. I get all my stuff into 1400 cu. in. and I wash daily, so that would just as easy for me for a month.

I agree with Lee. A 30L pack is just over 1800 cu. in., and as long as you pack well, you can certainly use that size pack for a month long trip. I have used that size for a trip that long before. I don't know if I could go down to 1400 cu. in. for a trip that long like Lee (though I have for shorter trips), but 1800 should be nice, light, and suit you well for your trip. But again, as Ken mentioned, it may be too small depending on how you pack and what factors you may have to consider: different weather, terrain, shoes, etc. So it's a judgment call. Enjoy your travels!