Snellen Acuity Converter

Visual acuity can be written several ways: US Snellen (20/20), metric Snellen (6/6), decimal acuity, and logMAR. This converter performs mathematical relationships among those notations so you can translate labels seen online or in records.

Conversions do not create new clinical measurements. A 20/40 notation from a phone chart is still only as trustworthy as that testing situation.

Follow these educational steps:

1. Enter one known value: 20-foot denominator, 6-meter denominator, decimal acuity, or logMAR.
2. Review the calculated equivalents and the explanatory notes.
3. Use related acuity library pages to understand what a given Snellen fraction means in plain language.
4. Do not treat converted numbers as an updated eye exam result.

If you enter 20/40, the tool shows related notations such as approximate decimal 0.5 and a corresponding logMAR value. That helps you compare literature that uses different scales.

Remember that two people with the same acuity number can still differ in contrast sensitivity, field of vision, and comfort.

The converter does not measure your eyes. It does not map prescription diopters to acuity.

It does not decide driving legality or disability criteria, which are jurisdiction-specific and clinically assessed.

Important limitations:

• Rounding conventions vary slightly among textbooks and electronic health records.
• Low vision notations and counting-fingers methods are outside this basic converter.

If you are trying to interpret an acuity written in your exam summary, ask your eye-care professional for context. Bring questions about daily function, not only the fraction.