I don't think there's a 'set' scale for jean sizing, especially since there's such a vast number of stores and brands out there. You should probably best off going into different stores and trying on different sizes.. I know one marketing technique, brands will have jeans that say 0 but really fit like a 3... It leads women to believe they're skinnier and all that... ANYWAYS I'm going so off-topic!

If it helps, I'm a size 3 / 26.