A dioptre is equal to the reciprocal of the focal length measured in meters.
The Power of a lens is the ability of a lens to converge or diverge light rays depending on its focal length.
The power of the lens is the ability of the lens to converge the rays of light falling on it. Definition: The power of a lens is the reciprocal of its focal length in meters.
When, f = 1 m, P = 1/f = 1/1 = 1 dioptre. 1 dioptre is the power of a lens whose focal length is 1 meter.