My personal rule of thumb on IH's sanforized denim is what little shrinkage you get from a soak/wash, you will get pretty close to that back in stretch after a few wears - except for the length of course. So I look at and follow the IH measurements and that has worked well for me. I have 4 IH cuts in different denims and have gone TTS (same tag size) on all. Usually it is pretty obvious which size is the best choice. On the 18oz raw denim I'd say there is a little more "art" involved, but the sanforized is pretty straightforward unless you are just right between sizes. Of course if you size way down, and put a lot of stress on the waist, you could get more stretch I'm sure. Some people might want to size down to get the look they seek but I have not had to do that.
Thanks for that – really helpful. I'm not a great fan of turnups -- I was planning on getting them hemmed to 34", the same as my existing pair. Does that sound like a good idea? I didn't realise they got shorter after being washed/soaked...
Also, RP, that looks to me an excellent fit post-soak. Didn't realise it made such a difference what with the sanforization and all that stuff. Really hope mine end up looking similar!