How Do I Tell What Power Magnification My Glasses Are?

Eyeglass lenses are determined by prescriptions which are put together by an eye doctor, based upon what type of vision deficiency you may have and what types of lenses can help you see properly. There are a number of ways to tell what magnification power your eyeglass lenses are, based on the prescribed information.

Prescription Letters

• Doctor's prescriptions for eye glasses are written in a specific way, so once you know what these prescriptions mean, you can determine the magnification qualities of your glasses. The letter in front of a series of numbers and slashes on the prescription will be R and L, standing for right and left. The following number will determine the magnification of the lenses needed for each eye, but it is important to know which eye pertains to which numbers, so you know if there is one lens with a stronger magnification quality.

Prescription Numbers

• Following the letters are numbers, which are the next clue as to the magnification ability of your eye glasses. The first number measures your long- or short-sightedness. These numbers vary in 0.25 steps up and down. These numbers can also be different for each eye. The second number measures your astigmatism, or the shape of your eyes to match the shape of the lenses. These numbers go up in .25 steps. If you have no astigmatism, your eyes are as round as a tennis ball.

  The final number on the prescription is called the Add. This is extra help for those filling the prescription to adjust your lenses over time.

Translation to Magnification

• To figure out the magnification of each lens, you must halve the second number on each equation and then add it to the first number. This will give you what optometrists call the "best vision sphere." Then you must take that number and add it to the Add number, giving you the magnification for each lens. These numbers rise incrementally by .25, with 0 being without magnification. Magnification is often different in each lens as one eye often needs more help than the other. But you now can determine what the prescription for the eye glasses would be if changed into magnifiers.