What does 20/20 vision mean?

It means you can read at 20 feet what a person with normal vision can also read at 20 feet. The top number is the testing distance; the bottom is the distance at which a normal eye can read the same letter.

What is the difference between 20/20 and 6/6?

6/6 is the metric equivalent of 20/20. Both represent 100% normal acuity — 6/6 uses meters (6 m / 6 m) while 20/20 uses feet (20 ft / 20 ft).

How is LogMAR calculated from a Snellen fraction?

LogMAR = log₁₀(denominator ÷ numerator). For 20/20 that is log₁₀(1) = 0.00. For 20/200 it is log₁₀(10) = 1.00. Better than normal acuity gives negative LogMAR values.

What is a normal LogMAR value?

LogMAR 0.00 corresponds to 20/20 (normal vision). Values below 0 indicate better-than-normal acuity; values above 0 indicate reduced acuity. LogMAR 1.00 (20/200) is the legal blindness threshold in the US.

How is percentage vision calculated?

Percentage = (20 ÷ Snellen denominator) × 100, or equivalently, decimal acuity × 100. 20/20 is 100%, 20/40 is 50%, 20/200 is 10%.

Can this tool be used for 6-metre Snellen charts?

Yes. Select "Snellen (m)" as the input scale and enter the denominator (e.g. 6 for 6/6, 12 for 6/12). The numerator is always 6 for metric charts.

Snellen Acuity Converter

Name: Snellen Acuity Converter
Availability: InStock
Author: Nham Vu

Convert visual acuity between Snellen (20/20 or 6/6), decimal, LogMAR, and percentage of normal vision instantly.

Enter Visual Acuity

Input Scale

Snellen Fraction (feet)

Numerator is typically 20 ft (testing distance)

Conversion Results

Enter a value and click Convert to see results.

Common Acuity Reference

Snellen (ft)	Snellen (m)	Decimal	LogMAR	%

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Summary

Convert visual acuity between Snellen (20/20 or 6/6), decimal, LogMAR, and percentage of normal vision instantly.

How it works

Select the input scale: Snellen (ft), Snellen (m), Decimal, LogMAR, or Percentage.
Type your value into the input field.
The converter calculates the equivalent in all other scales immediately.
Use the reference table to look up common standardized acuity levels.
Copy any output value with one click.

Use cases

Convert a 6/6 (metric) prescription to the American 20/20 equivalent.
Translate a LogMAR score from a clinical trial into a Snellen fraction for patient communication.
Check what percentage of normal vision a measured acuity represents.
Quickly look up where a patient's acuity falls on international classification charts.
Verify conversions when reading ophthalmology research papers.
Help patients understand their visual acuity report in plain terms.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu