How To Choose Corrective Lens & How To Choose Prescription Swim Goggles

How to determine your lens power for your goggles and diving mask

For use in the water (an already-blurry environment), step diopter (or diopter) is used to determine lens power for your swimming goggles and diving masks. The first step to choosing prescription goggles is determining the diopter strength that most closely matches your current prescription.

Formula is:

Sphere + 1/2 of the cylinder = Diopter strength

Sphere is the degree of weakness in diopters. This is always a negative number for nearsighted people, and a positive number for farsighted.

Cylinder is the degree of astigmatism in your eye. Add half of this number to the sphere to determine diopter strength.

For example:

O.D. (right eye)-4.50-1.25
O.S. (left eye)-5.00-1.00

Calculated Diopter strength is as below:

 Calculated Diopter StrengthDiopter Strength (rounded)
O.D. (right eye)-5.125-5.00
O.S. (left eye)-5.50-5.50

Due to water blurry environment and reflection, corrective prescription goggles and diving mask are normally manufactured as -2.0, -2.5, -3.0 and so on. Lenses are in increments of 0.5. We carry lenses ranging from diopter -1.5 to -10.0 and lenses are in increments of 0.5. Please contact us you have any queries.


If you have low astigmatism, say cylinder is less than 2.00, our corrective lenses will fit you well. It provides economic and quick way for you to see clearly in the water.

If you have high astigmatism, our corrective lens goggles may still a solution, but may not produce the best result as you wear prescription glasses. Our products provide an economic and fast way. It will satisfy the most of your purposes in the water. In the future we aim to produce custom-made products for the best visual results. At this moment, if you have any feedback, it is appreciated you can share it with us or contact us at if you have any queries.


  1. A general rule when choosing a diopter lens is to round down — rather than up. This is due to water reflection and it places less strain on your eyes.
  2. This measurement is only a suggestion. You may like to choose right diopter per your own experiences.
  3. Our products only cover Sphere with negative values.

Choose the Goggle Model

There are both recreational and racing styles of prescription goggles.

Serious swimmers and lap swimmers will want to buy a racing style and should look for low profile frames, or those with “racing” in the model name.

Swimmers who rarely do lap swimming and just want an alternative to going without glasses in the water — such as masks or goggles with larger lenses — should look at recreational models. These have more generously padded frames and offer wider peripheral vision.