snow / winter boots - size and comfort rating question

I haven't purchased snow boots before...

I bought some youth size Kamik boots off ebay (can't remember the actual model names). I bought them one size larger than their US shoe size. Since they're growing I wanted a little room in there.

The boots are "comfort rated" for -25F or -40F. How accurate are those comfort ratings???

My wife and I are also going to buy boots, probably off ebay since slightly worn boots will be fine for us to wear a couple of times per year. Should we buy one size larger than our normal shoe size?

Try this converter:
http://onlineconverters.com/shoes.html

But be sure to adjust for what you know of the sizings for whatever brands you're looking at. In my experience, Columbia runs a little big, Merrel runs a little small.

Sorrell recommends to buy up to the next size if you have a 1/2 size, to stay with your size if you are a full size. This has worked reasonably well for me. The one thing you don't want is a snug boot - need that dead air space.

Kamik seems to run about the same size as Sorrell. I don't know much about Columbia - although I know my wife likes the look of their boots.

SAB

Just bought a new boot. My old boot was a 28.5/324 and it was too tight. I bought another boot that they fit me for as a 28/325. So I bought a size smaller cause my last pair was too tight. Boot purchasing defies logic. Thank God for those giant hair dryers.