Oh, you meant the waist? I wear a 30 in most pant sizes (31 very occasionally), so I ordered them in 30W/28L. They are snug enough that a belt is entirely unnecessary, but not too snug to be noticeably tight or otherwise uncomfortable. If you're on the larger side of a 30W, I think you did right by ordering a 31.
Also got several of my items that I ordered online today. The Todd Snyder Cargo's are almost the exact same fit as the McNairys, though I'm pretty sure the leg opening on the Snyders is a tiny bit smaller. I also got the Saturday's White '&' T as well as the TS Camo T, both of which are too long for my tastes (I ordered them in mediums, will try smalls). Finally, I got the Ovadia & Sons cardigan and tie. I like the tie a lot, but will be returning the cardigan - I've seen better for the price.