At least wide enough for a chair under the counter. After that, it all depends on what you plan on having out on the counter and how you will be using it.

We are doing 18 inches without a drawer, due to space limitations, but the drawers from semi-custom cabinet lines are 24 " wide. Depends what you need.

You need a minimum of 24" to fit a sitting person. 30" is better so that you can twist from one side to the other to open drawers or whatnot. 36" is luxurious, but wastes space that could be used in a drawer stack if you don't have that room to waste.

Thanks everyone!

One other related question, my master bath cabinets will be comfort height (kitchen counter height). Would it be bad if I had the vanity all one height? I like the look of the single piece of marble/granite (don't know yet), and I could use a counter height backless stool.

Do you think that would work?

I'm in the middle of a complete new construction project, and I'm completely on decision making overload!

hi Laura
our architect drew in similar, a lower vanity section for makeup, but we had him redo it to make it all one height. I usually just stand up when I put on makeup and didn't want to break up the look of the granite. I may put in a stool in the bathroom and move it to the vanity area when I do want to sit, and use a hand mirror (magnified).

We're on overload too. Picked granite today now on to faucets and cabinets!

Nhbaskets, where did you buy your vanity?