Quick Glasses Rx Calculator
Enter values from your prescription to calculate spherical equivalent, transpose form (plus-cylinder ↔ minus-cylinder), and optional near sphere with ADD.
Right Eye (OD)
Left Eye (OS)
Educational use only. Do not order or change lenses without confirmation from a licensed optometrist/ophthalmologist.
How this glasses prescription calculator helps
If you have ever looked at your eyeglass prescription and wondered what all the numbers mean, you are not alone. This calculator converts your basic prescription values into a more readable summary. It is especially useful for checking spherical equivalent and understanding transposition between minus-cylinder and plus-cylinder notation.
What each prescription value means
Sphere (SPH)
Sphere shows the overall lens power for nearsightedness (minus values) or farsightedness (plus values). Example: -2.00 means mild to moderate myopia correction.
Cylinder (CYL)
Cylinder is the amount of astigmatism correction. It can appear as negative or positive depending on notation style. Many optometrists in the U.S. write in minus-cylinder format.
Axis
Axis describes the orientation of astigmatism correction in degrees from 1 to 180. Axis has no meaning without cylinder.
ADD
ADD is additional plus power used for near work in bifocal or progressive lenses. In this tool, if ADD is entered, an estimated near sphere is shown as SPH + ADD.
What the calculator computes
- Spherical Equivalent (SE): SPH + (CYL / 2)
- Transposed Prescription: new SPH = SPH + CYL, new CYL = -CYL, new Axis = Axis ± 90 (normalized to 1-180)
- Estimated Near Sphere (optional): SPH + ADD
Important limitations
This tool is for learning and quick checks. Real prescriptions also consider lens material, base curve, prism, monocular PD, fitting height, and frame geometry. Small mistakes can reduce clarity or cause eyestrain. Always verify your final prescription with your eye care provider.
Tips for better accuracy
- Enter values exactly as written on your most recent prescription.
- Use quarter-diopter increments (0.25) for SPH/CYL when possible.
- Enter axis only if CYL is non-zero.
- Keep axis within 1 to 180.
- Treat online calculations as a second opinion, not a replacement for an exam.
Frequently asked questions
Is spherical equivalent enough to buy glasses?
No. It is a simplification and does not replace full astigmatism correction.
Why transpose a prescription?
Different clinics and countries may write CYL in opposite sign conventions. Transposition keeps optics equivalent while changing notation style.
Can this calculate contact lens prescriptions?
Not reliably. Contact lenses often require vertex distance adjustments and brand-specific fitting data.