Well, I am not really sure what my regular size is, in jeans, to be honest! Because I have jeans in 3 different sizes from different companies and they all seem to fit -- although the fit differs, of course. But then the cut differs, too.
And I've found that even the same manufacturer's jeans in the same style can differ. For example, I have a pair of dark wash J. Crew toothpicks that I really like a lot. They have some poly in them but they feel really crisp. I "sized up" in them and got just a bit of ease, so they fit me more like cigarette jeans than skin tight skinnies. Well, I ordered the same jean in the same size in an ecru and it was AWFUL - this one was in that super soft stretchy fabric and I looked ridiculous in it -- it was like leggings, but baggy elephant skin leggings. Yuck.
What I can say is that I got the Kut Dianas in my regular size for GAP skinnies (2) and they fit me fine. Some people had suggested sizing down, others had suggested sizing up (because they are white) but in the end I was glad I went with what I got. They are a nice substantial fabric with a tiny bit of stretch -- 98% cotton, I believe -- and not lightweight or legging-like.
ETA: They fit me snugly at the waist/ hip (I couldn't size down or I would not be able to do them up on my hipbone) but there is a small amount of room elsewhere. I also like that they are not completely calf-sucking.