Professional Swimming Goggles: Size from 0 to+7. Because of the refraction under water, please choose 0.5-1 lower than your lens, not higher. If you have little difference between 2 eyes, like +4.0 and +4.5, you can choose a pair of +4.0 or If you have big difference between your 2 eyes, like +2.0 and +6.0, you can buy 2 pairs and assemble them.