I have two of the Blackhawk dress belts. One is black lizard the other is brown alligator. Most belts are sized from the point the buckle attaches to the middle hole as above. My belts measure exactly 42 inches from the buckle attachment to the center adjustment hole.
The most accurate method of determining the proper length is to take a measurement with the actual gear you will be carrying in place with your current belt. Put all your gear on and get it snugged and secure, as you would usually wear it. Note whatadjustment hole you are using. Take the belt off and measure from the buckle attachment to that adjustment hole. Whatever the measurment is, is the size you would need. If you measured 38 inches a size 38Blackhawk belt would allow you to fasten it at the center hole.
If you don't have all your gear available, you can measure from the buckle attachment to the current adjustment hole you use to keep your pants up, then add 2 inchesfor the IWB holster, but that is kind of a crap shoot.
The belts I have area tad more than 1/8th of an inch thick.They have some sort of internal stiffener and are much stiffer than similar sized leather belts that I have. They don't roll over or twist like some leather belts will do.
All in all, they are not bad for the price. They seem to be holding up fairly well. Iwear the black one with suits and dress slacks and the brown one with khakis and Dockers. I like/need to dress professionally a lot and don't really care for the "tactical" look. Don't get me wrong, I'm usually wearing a Wilderness Instructor belt when I wear jeans. But I go a lot places and do a lot of things where a suit or sportcoat is expected and I think these belts fit my needs at a very good price.
As far as needing a belt to carry IWB...I think I do...I feel the holster is more stable and secure. However, that is an indivdual choice based on body type, weapon size and weight, and your own personal comfort zone.
FWIW, I quit ordering from Optics Planet. I have tried to order items 3 times. Each time I was informed that they were out of stock and the backorder would take several weeks. You don't know if something is in or out of stock until you have placed the order.
Hope that helps!