Ours is 10.5" and I think it's just right. We don't have any appliances in the island though, no dishwasher or cooktop. Just a tiny little prep sink. Do you have any appliances in your island? To be fair, we haven't used our island yet so i'm not sure about the knee bumping issue.

Your island is 7'x3'...ours is 8'x3'. Honestly, I think it's plenty big, and I wouldn't make it bigger because I like having more breathing room.

The overhang on my peninsula is 10 inches and it works for us, but I think 12 would be great if you have the room. I don't think you really need 15 if you would rather have the space to walk around your island.

NKBA recommendations are:

Table-height (30" off finished floor): 18" overhang
Counter-height (36"): 15" overhang
Bar-height (42"): 12" overhang

Personally, I think the recommendations are right on. We have counter-height w/15" and it's fine (18" might have been even better, but we had space limitations). Friends of ours have 12" and I always have to sit sideways (my DH won't sit at theirs at all since it's too uncomfortable for him).

How wide are your aisles right now?

If you have counter-height seating, I strongly urge you to listen to your KD...she's right!

Hi, I have cabinets underneath the counter in the island, so the granite fabricator would only do 10 inches with no support. It's fine. We all fit, no one is hitting their knees. My husband is 6' 4". Great storage underneath.

For us, 15" is the magic number. My friend has 12" and like some others, it means we sit sideways and it's not so comfortable. I'm 5'8" and DH is 6'1" -- FWIW.

Here's another post on the same topic:
Depth of overhang for island

Thanks for the replies. I had read the other threads on this topic and still kind of wondered how people felt about the different depths. It clearly seems to boil down to personal choice. I can't believe no one is going to help me out and tell me what to do. ;-)

We have a curved overhang that is 12" at the ends and 15" in the center. I'm 5'8" and can sit comfortably at both. Keep in mind that when seated, the chair is pulled out a bit from the counter. Also, I tend to rest my feet on the bottom rung of the stool so they don't hit the cabinet.
I do like the way the stools fit under the 15" overhang better. I think it looks nicer to have the stool pushed all the way in. JMO, if you have the space go for the deeper overhang.

My current island has 8 inches overhang. I'm 5'8" and it's usable but could definitely be better. I think 12 inches would be perfect and that even 10 would be a big improvement on what I have now. I think that 15 would probably be wasted on us, not to mention that it creates more support issues if you're using granite. However, we also don't eat every meal at the island or sit there a long time. My understanding is that the higher the stools are, the less knee room you need because your legs are not angled under the counter the same way. Test it out! Like the other poster, I tend to sit with my legs on the bottom rung.

Our old island had 12" - the new one has 15"- both were counter height. 12" was usable. Basically you don't sit all the way scooted in or you sit a little sideways. The 15" is totally comfortable.

Of course if the space is more important to you as passage way, 12" would do.

We have 15" and find it very comfortable. I have long legs, and I'd be uncomfortable with less. I also like that my stools can be stored completely under the overhang.

We have 14.5" (had wanted 15" but granite slab was not large enough) with counter height seating. I am tall and it's fine, but 15" would be better. And like holligator, my backless stools store underneath the overhang.

I will be contrary and say that our old kitchen had 18 inches and we are sticking with that. We're not that tall (I'm 5'4") and hadn't really thought about it, but when we measured the old kitchen before demo we realized it was a full 18 inches. I like the added space, but obviously haven't tried the smaller space. Anyway, in our case we have the room that the additional inches aren't a problem. To the OP, can you try out a friend's island or mock something up with boxes and see what feels comfortable to you? It seems like there are a lot of different preferences.

Our island will be at 36" height and KD originally spec'd 12"; my DH, who is 6'3", really lobbied for a deeper overhang and we are going to 15" for increased comfort level on that end. We will have to use corner supports now, but he has compromised on so many other areas in this kitchen that I will live with those.

I'm 5'10, hubby 6'5 and we fit at a 12" overhang just fine. We don't feel the need to push our chairs in so far that our knees bang on the cabinets. We push in until we're comfortable and it seems fine. If you have the 15" I'm sure that would be better but 12 is sufficient, at least for us.