With this online calculator you can compute the power of the contact lenses you from the power of the glasses you already have. For example this could be necessary if you would like to buy soft lenses over the internet. Despite the fact that you can buy your contact lenses online you will still need to go to an optician for checkups. An optician need to check your eyes on vascular growth into the cornea, infections and scarring if you wear contact lenses.

You can also compute the opposite: given the power of your contact lenses you can compute the power of the glasses you will need. In addition you can do the same two calculations for glasses on an unusual distance from the eye. For instance for glass(es) of a diving mask that are further away from the eye than the standard distances of 12 and 14 mm.

First enter the known power: of your current glasses or lenses. Choose plus for hyperopia (far-sightedness) and minus for myopia (near-sightedness). Then choose the type of glasses or lenses you have now. There are two types of glasses: those at 14 mm distance from the eye and those at 12 mm distance from the eye. Finally you can enter the extra distance, for instance for the glasses of a diving mask . This is optional.