Prescription Decoder
Glasses Atlas · Free tool
Prescription decoder
Type the numbers from your glasses prescription and get a plain-English reading, plus which lenses actually suit it. No email, no sign-up.
Leave a box blank if it is empty on your prescription. ADD and PD are optional.
What the numbers on your prescription mean
The short version: the sphere (Sph) sets your main correction and its sign tells you nearsighted (minus) or farsighted (plus). Cylinder (Cyl) and Axis correct astigmatism. Add is extra power for reading. PD centers the lenses over your pupils. Higher numbers are not worse in any moral sense, they just mean a stronger correction.
| Abbreviation | What it means |
|---|---|
| OD / OS | Right eye (oculus dexter) and left eye (oculus sinister). |
| SPH (Sphere) | Main lens power in diopters. Minus is nearsighted, plus is farsighted. |
| CYL (Cylinder) | The amount of astigmatism correction. Blank means no astigmatism. |
| AXIS | The direction of the astigmatism correction, from 1 to 180 degrees. |
| ADD | Extra reading power added to the bottom of the lens for presbyopia. |
| PD | Pupillary distance in mm, so the lens centers over your pupil. |
Prescription decoder FAQ
Is a higher prescription number worse?
Not worse for your health, just a stronger correction. A higher sphere means thicker lenses in standard material, which is why strong prescriptions benefit from high-index lenses to stay thin and light.
How do I know if I have astigmatism?
If the Cyl and Axis boxes are filled in, you have astigmatism. It is a common, harmless uneven curve of the eye that a cylindrical lens corrects fully.
Do I need high-index lenses?
Mainly if your prescription is strong. As a rough guide, standard lenses stay thin below about 2 diopters, high-index 1.60 to 1.67 suits moderate prescriptions, and 1.67 to 1.74 suits strong ones.
What is a normal PD?
Most adults fall between 54 and 74 mm, averaging about 63. Your own measured number is what matters, since it centers the lenses over your pupils.
Last updated: August 5, 2026 · Glasses Atlas Team · More free tools · Read your prescription in full
