I would have to say that it's definitely too big for a sgian dubh.

I ordered a cheap "Sgian Dubh " a while back thinking I would tear it apart to make my own however, with an overall length of 10" it looked like i had a plank in my hose rather than a small knife. The site I ordered it from said it was a sgian dubh but the box it came in had it labeled as a dirk. It would have cost more to send it back than it was worth so now I have this monstrosity of a knife.