38R comes with 32 waist pants. BUT...

[T900]

but if your waist is 30.5, would you buy the 38R jacket but go with the 30 inch waist pants?

would that spoil the overall flow of the suit e.g. pants too narrow for jacket?

i heard that the max the tailor can take in for the waist is 1 inch without the back of the trousers pluckering.

 

[Jovan]

Get the 30" pants and have them let out a bit if need be. I'm technically a 32", but even then I've had to take in pants that were supposedly that size.

 

[twblalock]

Well, unless the 32 fits your seat and thighs better. If that is the case, you should take the 32 in.

Pick the pants that fit the best there and then adjust the waist to match your own.

Nothing worse than a guy who should be wearing larger pants being shoehorned into a smaller size because of waist. I have this problem, it can look pretty bad.

 

[Holdfast]

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.