Perimeter, Area, and Fit Ellipse in Image J

[Geology Guy]

Good Morning Everyone,
I have images with round particles in them that are almost pretty much ellipse to circle in shape. I will like to measure the SIZE of these objects in Image J. I have read the manual but still not sure if Area, Perimeter or Fit Ellipse would be the best way for me to measure the SIZE of these particles. Thanks for your replies.