What is the difference between Diopter and Magnification?

Diopter refers to the curvature of the lens. As the diopter increases, the lens become thicker and the curvature greater. As the curvature increases, light rays are redirected to fill a greater portion of the viewer’s retina which makes the object look bigger.

Powers refers to how much larger an object is made to look through a magnifying lens. Power is typically indicated by an X such 2X or 4X.

While there is more than one formula to convert the diopter of a lens into its power, the most common formula is this:

Magnification = (Diopter / 4) +1

For example an 3 diopter lens makes an object look 75% larger, over and above what the unaided eye already sees.

Note - As you increase the magnification, the lens size effectively decreases. It is not possible to get a high power lens in a large diameter. Combinations are a compromise for  the “ideal” magnifier.