My honest opinion, speaking as a pro photographer and lover of bodies male and female, is that your cock looks to be in very nice proportion with your body. Therefore, if you a very small guy (like Prince, for instance) your cock might be as small as 5" or less. But if you are a big guy (like Arlold Schwarzenegger) your cock might be 8" or 9". Either way, it looks like a damn fine cock, and will always impress as long as you keep that body of yours nice and firm. Only you know if it's the sort of size that YOU consider big or small. My instincts tell me that you are between 5'6" and 5'8" and that your cock measures just under 6" long x nearly 5" mid shaft girth. ie it is an above average size. (How did I do?)
Every one has their own opinion of what's big or small. I consider big to be as big or bigger than mine, ie.7+" long, and small to be anything below about 5.5" long. But I think it's relative to size of body. A friend of mine is a slim 6'3" and only has a 4.5" erection. It looks tiny on him, but it would look fine on a another friend who is a skinny 5'1". The latter guy has 5.5" which looks pretty big on him.