Based on some measurements from pics. I would say Mandingo is no doubt 11inch plus if not really close to it and is bigger than 10 inches without a doubt.
Everyone keeps putting hands as a source for measuring, 2 fist, 3 fist, it is just not consistent. Small girls have tiny hands, tall girls have big hands usually, too many variations in hand size. One thing you can rely on that is almost always the same size or pretty close in size is the size of the head. The average female head vertical length from the tip of the chin to the top of the head is 8.6". 95% of all women have this part of the head between 8.3" to 9.1".
Knowing this, all you have to do is take pictures that have Mandingo getting a blow job. The picture's angle should be one where they are at around the same distance parallel to the camera so that you the his dick won't be a lot closer in the shot making it bigger when you measure it. You want to do the same where his dick and the chicks head isn't a lot closer to the cam, cuz then that won't give him justice. Once you find a picture like this, take a ruler and take the measurements of the girls head and his dick.
His dick is always a lot longer so you automatically know it is much bigger than 8.6". Take the measurement of the length of his dick and minus it from the length of the girls head (from chin to top of head). Do some simple math, take the difference and divide it by the size of the girl's head. What ever percentage you get times it by the average head size of 8.6" then add it. I did it with 3 pictures and came out between 10.5" - 11.31". That averages just shy of 11".
So that is that. By the way he was between 28% to 33% longer than the 3 girls head. That is how I came up with my figures.
Yes I was very bored when I came up with this math, lol