Hello,
Me and my friend are going to take a 700km trip from Stockholm to Copenhagen. We have never done a trip this long before and therefore can't decide on a trunk bag.
We're aiming to ride it in 6 to 7 days and we want to pack as light as possible. We will bring a small two person tent and NO cooking equipment I think i only want a trunk bag (3 piece bag). Based on this criteria, how many liters should the bag be? can i survive on a 35Liter trunk bag?

Thanks,
Sebastian.

That's not a long trip. I'd recommend simply a handlebar bag and some small rear panniers. Strap the tent and sleeping bag to the top of the rear rack in a dry bag.

I don't see the point of the 3 piece trunk bag/pannier combination bags. It wouldn't work for me.

I'd start by listing what you are taking with you and seeing how big a bag it fits in.

Since you've never done this before, you will likely require less than you think in terms of clothes, both on and off the bike. When I tour, I take 1 pair of lightweight pants (trousers), 1 wool t-shirt, 2 biking wool biking jerseys, 2 pair of biking shorts, 2 pairs of socks, biking shoes and walking shoes. Oh, and 2 pair of quick drying underwear (pants). Are you taking more than that?

Remember that racks made of metal and panniers are heavy. The larger the bag, the heavier the bag.

CGOAB is also laden with list-makers https://www.crazyguyonabike.com/