I'm 5'-8" and usually end up around 28.5" plus or minus a quarter inch. I take my time in the mirror and it usually requires two fittings for my tailor to get it right. For me I need to take into account the degree of waisting in the jacket and how my lower back and butt is silhouetted, and the trimness of the trousers at the thigh. It's all by eye for me, and I have taken the jacket back for tweaking after wearing it a while and noting the look from 20 feet away. It's all about balance.