Originally Posted by T900
but if your waist is 30.5, would you buy the 38R jacket but go with the 30 inch waist pants?
Welcome to my world (actually I'm about a 38S but with the same waist measurement as you).
You have a few options:
1) Shop around and try different sizes. Different cuts mean different suits and different sizes may work better for you. Some have less vanity sizing than others. I find a Brioni 38S with its 32" trousers needs a bit less tailoring on the waist that other trousers which claim to be 32. Also, try on the 30" trousers and see how they look. Also, some Loro Piano 36/30 works for me, with a little tailoring.
2) Try a 37/31 suit. RLPL 37S is an absolutely perfect RTW fit for me. Rare to find such a size, but perfect.
3) Go MTM/bespoke and forget about such worries and enjoy the larger than average drop. The only RTW I buy nowadays is RLPL, Brioni and occ. Loro Piano, for reasons I've already mentioned, plus I love their respective stylings.