Dioptre is the SI unit for measuring the power of a lens.
The power of the lens is known as the inverse of the focal length of the lens measured in meter(m).
To find the power of a lens in Ray Optics, the following formula can be used.
Power of lense = 1/ focal length in meter.
If the focal length is given in meters (m), the power of the lens is measured in Diopters (D), as in the unit of power of the lens is diopter. For a converging lens, the optical power is positive and for a diverging lens, it is negative.