It varies by state what is considered concealed, and in many states it is not defined at all. The legal definition that comes immediately to mind is in Arizona, where it is open carry if any part of the gun or holster is visible.
Many people (including LEOs) use different rules of thumb, but I do not know how much weight they carry. Some of the ones I have heard include:
- -It is easily recognizable as a gun. For example, in Virginia it is generally accepted that it is open carry for the purpose of restaurant carry if the grip is clearly visible, even if you are carrying in an IWB holster.
-The gun is visible from 3 sides of the carrier.
-More than 50% of the gun and holster is visible.
My feeling is that you shouldn't worry about it as long as you are legal to both carry openly and concealed in the state where you are. If it is a state where you are only legal if you open carry, I would carry in an OWB holster with the entire gun visible, just to avoid any ambiguity.