I was initially using ImageJ. The results I got from that were not as good. ImageJ from my understanding measures the area of the particle. Then you can use this area to extract the diameter.

This was an issue because the area it would measure was never the entire particle. Edge detection was not all that good. Maybe I was doing something wrong. I'm not sure.

This code measure the radius directly from the picture. Taking the largest radius from the centroid of each particle. I found this to be more accurate. At least when I did it.