FreeImgFix.com

Glasses Diopter & Acuity Unified Calculator

Convert complex prescriptions, calculate visual acuity units, and estimate ADD power. Use safely and securely right in your browser.

100% Local Processing (No Server Transmission)

Visual Acuity Converter

Common in Europe & Asia

20 /
6 /

Research & Clinical Standard

Glasses ➔ Contact Lens Diopter Conversion

Converted Contact Lens Power

SPH (Sphere) -
CYL (Cylinder) -

💡 Tip: Conversion is negligible below -4.00 Diopters.

※ This result is a calculation based on optical formulas. Use the same Axis (Cylinder Axis) as your glasses prescription.

Age-Based Presbyopia (ADD) Predictor

Estimated ADD Power Reading correction needed
+0.00 D

* Based on typical average data (e.g., Hofstetter's formula). Actual needs may vary based on individual accommodation.

Astigmatism Prescription Transposition

Why is Power Conversion Necessary?

Glasses sit approximately 12mm from the eye (the Vertex Distance), while contact lenses rest directly on the cornea. This difference in distance significantly impacts the effective power, especially for prescriptions of -4.00 Diopters (D) or higher. Use this tool to accurately adjust your power.

Additionally, if your prescription uses a different format (Plus vs. Minus cylinder), the Transposition feature ensures you can quickly verify your power in the standard format used by your practitioner.

Secure Local Processing

The FreeImgFix Vision Tool does not transmit any of your prescription data to an external server. All calculations are handled instantly by the JavaScript engine within your browser.

  • Full protection of Personal Health Information (PHI)
  • Works offline (after the initial page load)
  • Zero data usage for calculations