if you are wearing it lower than normal, then it might be a wee short. The main consideration is if you like it that length or not. I usually consider it long enough it the endge hits my kneecap somwhere, top, middle or bottom. Above the kneecap is too short ( for my tastes ) but I have seen a great many pics, both current and historical where the "hem" of the kilt falls just above the kneecap.

as long as you are comfortable with it, and it isn't painfully high, I'd say it's fine. If you can see thigh, it is probably way too short.