What does LogMAR mean?

LogMAR stands for "logarithm of the Minimum Angle of Resolution." It measures the smallest angle (in arc minutes) the eye can resolve. A LogMAR of 0.0 equals perfect 20/20 vision; positive values indicate worse acuity and negative values indicate better-than-average acuity.

What is 20/20 in LogMAR?

20/20 Snellen equals LogMAR 0.00, decimal 1.0, and 100% vision. It represents the normal reference acuity at which a person can read a letter that subtends 5 arc minutes at 20 feet (6 meters).

What is the legal blindness threshold?

In the United States, legal blindness is defined as best-corrected visual acuity of 20/200 or worse in the better eye. This equals LogMAR 1.0, decimal 0.1, or 10% vision.

Why is LogMAR preferred in clinical research?

Unlike Snellen fractions, LogMAR values are evenly spaced on a logarithmic scale, which means arithmetic operations (averages, standard deviations) are statistically valid. Each line on a standard logMAR chart corresponds to a change of 0.1 log units.

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

Both express the same acuity; the only difference is the test distance unit. 20/x uses feet (standard in the US), while 6/x uses meters (standard in the UK and most other countries). 20/20 and 6/6 are the same acuity.

Can LogMAR be negative?

Yes. A negative LogMAR value means better-than-normal acuity. For example, LogMAR -0.1 equals Snellen 20/16, meaning the person can resolve detail that a person with normal vision can only resolve at 16 feet.

LogMAR Visual Acuity Converter

Name: LogMAR Visual Acuity Converter
Availability: InStock
Author: Nham Vu

Enter a visual acuity value in any format and instantly convert it to LogMAR, Snellen (feet and meters), decimal, and percentage.

Enter Visual Acuity

Input Format

LogMAR (e.g. 0.0, 0.3, 1.0) Snellen feet — 20/x (e.g. 20, 40, 200) Snellen meters — 6/x (e.g. 6, 12, 60) Decimal (e.g. 1.0, 0.5, 0.1) Percentage (e.g. 100, 50, 10)

Value

Conversion Results

Enter a value and press Convert to see results.

Quick Reference

LogMAR	20/x	6/x	Decimal	Note

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Summary

Enter a visual acuity value in any format and instantly convert it to LogMAR, Snellen (feet and meters), decimal, and percentage.

How it works

Select the input format you already have (LogMAR, Snellen 20/x, Snellen 6/x, decimal, or percentage).
Type your measurement into the input field.
The converter instantly calculates all equivalent values in every other format.
Use the Copy button next to any result to copy it to your clipboard.
Common reference values (20/20 normal, 20/200 legal blindness) are shown in the quick-reference table below.

Use cases

Convert a research paper's LogMAR values to familiar Snellen fractions for clinical discussion.
Translate a patient's 20/x chart result into decimal for international medical records.
Check whether a LogMAR score meets the legal threshold for low vision or blindness.
Cross-reference visual acuity across multiple study formats when reviewing literature.
Quickly look up standard Snellen equivalents for common LogMAR milestones.
Prepare optometry reports that require both LogMAR and Snellen notation.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu