Just added a screen capture from the nest with male and female Osprey labelled.
The Audubon Shop posted this about the Osprey this morning
Concerning Osprey: "Within populations, females average about 15–20% larger in body mass than males, and 5–10% longer in wing, tail, claw, and bill length. In addition, females tend to have fuller, darker breast-bands and darker heads than males, although this varies among populations." (excerpt from an article by Alan F. Poole)
Generally people look for what is referred to as the "necklace" of darker feathers on the breast of the female as an easy way to distinguish them.