Glasses to Contact Lens Prescription Converter
Convert eyeglass prescriptions to contact lens prescriptions with accurate vertex distance calculation
Right Eye (OD - Oculus Dexter)
Nearsighted (-) or Farsighted (+)
Astigmatism correction (optional)
0-180 degrees (required if CYL)
Left Eye (OS - Oculus Sinister)
Nearsighted (-) or Farsighted (+)
Astigmatism correction (optional)
0-180 degrees (required if CYL)
Important Medical Disclaimer
This calculator provides an estimated power conversion based on the standard vertex distance formula. However:
- Contact lens prescriptions require additional measurements (base curve, diameter) that can only be determined by an eye care professional
- Always consult with an optometrist or ophthalmologist before purchasing contact lenses
- Professional fitting is essential for eye health and comfort
- This tool is for reference purposes only and does not replace professional eye care
When to Use This Converter
Online Contact Lens Shopping
Get a reference conversion before ordering contact lenses online. Understand how your glasses prescription translates to contact lens power for better purchasing decisions.
First-Time Contact Lens Wearers
Understand the difference between your glasses and contact lens prescriptions before your first eye exam for contacts. Know what to expect during the fitting process.
High Prescription Powers
Essential for prescriptions beyond Ā±4.00D where vertex distance correction significantly affects the required contact lens power. Avoid ordering incorrect powers for high myopia or hyperopia.
Educational Understanding
Learn how vertex distance affects prescription power and why glasses and contact lens prescriptions differ. Understand the optics behind the conversion for informed discussions with your eye doctor.
Prescription Verification
Double-check your eye doctor's contact lens prescription conversion. Verify that the vertex distance adjustment was properly applied for accurate vision correction.
Astigmatism Corrections
Convert complex prescriptions with cylinder and axis values for toric contact lenses. Understand how each meridian is adjusted separately for accurate astigmatism correction.
Frequently Asked Questions
Can I use my glasses prescription for contact lenses?
Not directly. While lower prescriptions (below Ā±4.00D) may be similar, higher prescriptions require vertex distance adjustment because contact lenses sit directly on your eye while glasses sit about 12mm away. Our calculator automatically applies the correct conversion formula based on your prescription power.
What is vertex distance and why does it matter?
Vertex distance is the space between your eye and the back surface of your eyeglass lens, typically 12mm. This distance affects the effective power of the lens reaching your eye. Since contact lenses sit directly on your eye (zero vertex distance), the prescription power needs adjustment for prescriptions beyond Ā±4.00D to maintain the same level of vision correction.
Is this converter completely free to use?
Yes, our Glasses to Contact Lens Prescription Converter is completely free with unlimited conversions. No registration, payment, or subscription required. However, always consult with an eye care professional before purchasing contact lenses to ensure proper fit, base curve, diameter, and overall eye health.
How accurate is the conversion calculator?
Our calculator uses the standard optometric formula Fc = F / (1 - dF) recommended by eye care professionals worldwide. Results are automatically rounded to 0.25D increments, matching standard contact lens power steps. While highly accurate for power conversion, professional fitting is still essential as contact lens prescriptions also require base curve and diameter measurements.
What do SPH, CYL, and AXIS mean on my prescription?
SPH (Sphere) indicates the lens power for nearsightedness (negative values) or farsightedness (positive values). CYL (Cylinder) measures the degree of astigmatism correction needed. AXIS (measured in degrees from 0-180) shows the orientation or angle of the astigmatism correction. If you have a CYL value, you'll need toric contact lenses designed for astigmatism.
When do I need vertex distance conversion?
Vertex distance conversion becomes important at Ā±4.00D and above, and is mandatory for Ā±6.00D and higher. For prescriptions below Ā±4.00D, the difference between glasses and contact lens power is typically less than 0.25D and may not significantly affect your vision. Our calculator automatically indicates when conversion is necessary and by how much the power differs.
Can I buy contact lenses with this converted prescription?
While our calculator provides accurate power conversion, a complete contact lens prescription also requires base curve (BC) and diameter (DIA) measurements that can only be determined by an eye care professional during a proper fitting. These measurements ensure the lens fits your eye properly and maintains comfort and eye health. Always get a professional contact lens exam and fitting.
Does the converter work for astigmatism prescriptions?
Yes, our calculator fully handles astigmatism by converting both principal meridians (SPH and SPH+CYL) separately when vertex distance adjustment is needed. The AXIS value remains unchanged as it represents the orientation of correction, not the power. The results are suitable for toric contact lens reference and show how each meridian's power is adjusted.
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