Depends on the height of the counter. I'm pretty sure NKBA says counter height is 15", bar height is 12".

As the previous poster mentioned, 15 inches is recommended for counter height bar.

However, we currently have 10 inches in a 42 inch height bar and it's tight feeling, but it would work for a minimum.

At 10" you wont' be able to tuck bar stools under it. They'll stick out, so you might as well go larger because the bar stools will be occupying the space anyway.

If you're trying to skimp on overhang b/c of aisle width...it won't work. People take up the same amount of space b/c you can squeeze your body in just so much! What you get when you skimp on seating overhang is uncomfortable guests...they have to sit farther away from the counter OR they have to "straddle" the cabinet OR they have to sit sideways...none of which are comfortable.

Well...I WAS going to link the NKBA Planning Guidelines, but apparently they no longer allow us to see them! You have to pay to join...not going to happen here! Plus it appears not just anyone can join...

Bottom line...the NKBA recommends a minimum overhang of... Table-height seating (30" high): 18"
Counter-height seating (36" high): 15"
Bar-height seating (42" high): 12"

Note this is a "minimum", not a "maximum". Your "counter guy" doesn't seem to know this. What about your KD? S/he should know this...

Having sat at many a bar, and a few counters, I can't see where the distance makes much of a difference. The choice of a stool or chair and the size of them could be a factor. Generally speaking, the average person needs about 11 to 12 inches of clearance as a minimum if sitting on a stool or small chair. 10 to 11 inches is also the maximum you can go to cantilever 3cm granite with out support. We have an average 10.75 inches unsupported clearance using stools, and have no problems with peoples knees hitting.

I just measured ours end to end, and it is 13 inches. It works fine for us. Since the bartop is on an entryway to the kitchen, we were worried that if it were longer, we'd keep bumping into it.

We use this area a lot, so it was great decision to put it in. This pic is just after it was installed.