[QUOTE=Zelda_K;518406]I tried the yoga mat method, but it didn't work for me. maybe i should have been sitting there a bit longer, will try again./QUOTE]

I was semi-successful using a mat. I folded it in fourths and put it on my dining room table, which has a marble top. The impressions don't last for long but I was able to get a outside to outside measurement that is similar to what I got when I just took a tape measure to my up-ended butt.

It looks like I'm measuring around 130-135 mm. My current saddle is 155 (or maybe 160?) and it's comfortable for me, so that makes sense.

BTW my current saddle is pretty close to perfect, but is wearing out (cover is cracking) so I need a new one. Sadly they don't make the one I have anymore, so I'm going to post pics of it in a separate thread in the hopes that someone can point me towards a new one with a similar shape.