Enter your prescription numbers and instantly understand what they mean — in plain English.
🔍 What Does My Prescription Mean?
Enter the values from your prescription slip. You'll get a plain-English explanation of your vision condition, prescription strength, and estimated uncorrected visual acuity.
👁️ OD — Right Eye
D
D
👁️ OS — Left Eye
D
D
🎉 Now you understand your prescription — order glasses online with confidence!
All tools on PDCalculator.net are for educational and informational purposes only. They do not replace professional eye care advice, diagnosis, or treatment. Always consult a licensed optometrist or ophthalmologist before purchasing eyewear or making any changes to your vision correction. Results are based on standard optical formulas and are provided as a general guide only.
📋 What Do the Prescription Abbreviations Mean?
SPH
Sphere
Main vision correction strength. Negative = nearsighted, positive = farsighted.
CYL
Cylinder
Astigmatism correction. How much and in which direction your eye is non-spherical.
AXIS
Axis
The angle (1–180°) at which the cylinder correction is applied.
ADD
Addition
Extra magnification for reading. Found on progressive/bifocal prescriptions.
OD
Right Eye
Oculus Dexter — Latin for right eye.
OS
Left Eye
Oculus Sinister — Latin for left eye.
❓ Frequently Asked Questions
Is a −1.00 prescription considered strong? +
No. −1.00 is considered mild nearsightedness. Most people in this range can see fairly well up close without glasses but struggle with distance. The scale generally runs: mild (0 to −3.00), moderate (−3.00 to −6.00), strong (−6.00 and beyond).
What's the difference between nearsighted and farsighted? +
Nearsighted (myopia) means you see clearly up close but blurry at distance — indicated by a negative SPH. Farsighted (hyperopia) means distance vision may be clearer but close-up can be blurry — indicated by a positive SPH.
What does 20/20 vision actually mean? +
20/20 means you can see at 20 feet what a person with normal vision sees at 20 feet. 20/40 means you need to be at 20 feet to see what a normal person sees at 40 feet — worse than average. 20/10 is better than average.
I have the same SPH number but different CYL — what does that mean? +
The CYL value indicates astigmatism, which is a different issue from nearsightedness or farsightedness. You can have nearsightedness (SPH) and astigmatism (CYL) simultaneously. They are corrected independently.