I found the sizing to be US 8 (the equivalent is UK 12). In terms of a size US 8, I would say it is true to size--mostly my range is 6,8,10 depending on brand. The waist is really high rise and the back waistband has elastic in it so you get that square look from behind, with a little bagginess at the top of the rump. Just beware that in that sense they aren't fashionable but might be fine for the hike.
All sizing on our website is in US sizes unless otherwise indicated on the specific product page.