Free Tool
Vertex Distance Calculator
Convert your glasses prescription to contact lens powers instantly. Uses the clinical 12 mm vertex distance standard.
Right Eye (OD)
Right Eye (OD)
Enter sphere power to see results
Left Eye (OS)
Left Eye (OS)
Enter sphere power to see results
Vertex distance: 12 mm · Conversion applied where |power| ≥ 4.00D · Rounded to nearest 0.25D · Scroll the mouse wheel over SPH or CYL to step in 0.25D increments
How Vertex Conversion Works
Your glasses sit roughly 12 mm in front of your cornea. That gap — the vertex distance — changes how strongly the lens must focus light to hit the same point on your retina. A contact lens sits directly on the eye, so its power must be recalculated to achieve the same optical result.
For prescriptions below ±4.00D the difference is clinically insignificant and the power passes through unchanged. For stronger prescriptions, the conversion formula is:
Results are rounded to the nearest 0.25D — the standard manufacturing increment for contact lenses. Axis passes through unchanged as it is not affected by vertex distance.