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>log in to commentI built this tool to quickly convert glasses prescriptions to contacts (and vice‑versa) using vertex distance, handling sphere, cylinder and axis. It shows the raw theoretical power in 0.25 D steps without any sign‑up. Let me know if it’s useful or what could be improved 😊
VertexLensCalc converts eyeglass prescriptions to theoretical contact lens power (and vice-versa) using vertex distance formulas.
- for
- Optometrists, eye-care professionals, and individuals needing prescription conversions.
- pricing
- free
Key features
- Glasses ↔ Contacts conversion — Calculate theoretical lens power in both directions using entered SPH, CYL and axis.
- Astigmatism support — Handles cylinder and axis values to convert toric prescriptions.
- Adjustable vertex distance — Default 12 mm, accepts 10–14 mm for more accurate results.
- 0.25 D display steps — Shows rounded power in standard 0.25 diopter increments alongside raw values.
- No sign-up required — Instant access to the calculator without creating an account.
- Formula transparency — Displays the vertex formulas used for forward and reverse conversions.
Use cases
- Convert a myopic eyeglass prescription to a contact lens equivalent for ordering lenses.
- Determine the theoretical glasses power from an existing contact lens prescription.
- Check how astigmatic (cylindrical) corrections change when moving between glasses and contacts.
VertexLensCalc. FAQ
Do I need to sign up to use VertexLensCalc?+
No, the tool is available instantly without any sign-up.
What formula does the calculator use?+
Glasses→Contacts uses Fc = Fs ÷ (1 − d × Fs); Contacts→Glasses uses Fs = Fc ÷ (1 + d × Fc), where d is vertex distance in metres.
Can I use the result to order contacts directly?+
No, the output is a theoretical optical estimate and does not constitute a prescription or specify lens brand, base curve, or fit.
Does the calculator handle astigmatism?+
Yes, you can enter CYL and Axis; the tool converts both principal meridians and rebuilds the cylinder.
What vertex distances are accepted?+
The calculator defaults to 12 mm and accepts values between 10 mm and 14 mm.
Is the tool suitable for high prescriptions?+
It accepts SPH from −30 to +30 D and CYL from −10 to +10 D, but results are theoretical and should be confirmed by an eye-care professional.
Summarized by DevHunt from vertexlenscalc.com · Oct 6, 2026. Details may change; check the official site.
