How many wide-mouth nalgene canteens and what size?

How many wide mouth Nalgene canteens would you carry for a 3 day winter trip

Sounds like an arithmetic problem to me. (Daily water needs divided by how many times per day you expect to be able to make water).

Regarding size, I lean towards 1 liter containers. I bring two one liters plus the 1/2 liter mentioned below and expect to make water morning and evening (except the first and last morning usually)

maybe a 1L bottle for keeping inside your jacket against your chest.

I use a 1/2 liter platy in a fleece pouch hung from my neck. I find a liter too heavy for that use but YMMV on that count. The half liter comes to bed with me, nice for wetting a dry mouth and also nice to have warm water for the first drink of the morning. I also find that I can more often make it through the night without a trip to the pee-tree if I sip during the night rather than cameling up before bed.

I used one 1 liter wide mouth nalgene softside over one should and around my neck using a one inch nylon strap. It worked well.

I also used another 1 liter container, just not a nalgene and put reflectix around it and buried it in my pack.

I use platys but I carry a 2L in my hydration compartment of my pack and a 600ml

I second the ideal of carrying a larger, 1.5 liter platy or soft sided nalgeen in your packs hydration reservoir. The water will generally be kept from freezing by your packs contents and your body heat.

I also carry a 32 ounce gaiter aid bottle on my pack for drinking out of. When I drain the bottle I refill it from my reservoir in my pack.

Of course I'm now carrying 2.35 liters of water which can be heavy but I justify it by not having to stop as often to melt snow for drinking water except in the morning and in the evenings. This way I can maximize my time hiking and minimize my time sitting around a stove.

I carry 2x 1.5L canteens. One is folded up in my pack as backup, the other rests underneath a jacket on top of my hipbelt.

I'm thinking 1.5 L Nalgene wide mouth inside our hydration compartment, which should help insulate it, and a 1 Liter Nalgene wide mouth or Platy, or .5 Platy, inside our jackets.

To keep things to our body proportions, weights and water needs (I'm 1.5x my wife's body weight), my wife could size down a bit – so if I carry a 1 L inside my jacket, perhaps a .5 L would be more appropriate for her inside her jacket.