20/20 Vision Calculator for 2020

Convert a Snellen acuity fraction like 20/20 or 20/40 into decimal acuity, minimum angle of resolution (MAR), LogMAR, and a plain-language vision category.

Quick Facts

Formulas
Decimal = num/den, MAR = den/num, LogMAR = log10(den/num)
20/20 gives a MAR of 1 arcminute and a LogMAR of 0 - the reference for normal sharpness.
Reference
20/200 or worse = US legal-blindness threshold
Measured in the better eye with best correction; 20/40 is a common US driving minimum.

Your Results

Calculated
Decimal acuity
-
numerator / denominator (20/20 = 1.0)
MAR
-
arcminutes; denominator / numerator
LogMAR
-
log10 of MAR; 20/20 = 0.00
Vision category
-
General reference band

Ready

Enter your Snellen numerator and denominator, then press Calculate.

About the 20/20 Vision Calculator

Visual acuity is written as a fraction such as 20/20 or 20/40. The top number is the distance you stood from the eye chart (20 feet, or 6 meters in metric); the bottom number is the distance at which a person with normal sight could read the smallest line you managed. This calculator converts that Snellen fraction into the three measures clinicians use - decimal acuity, minimum angle of resolution (MAR), and LogMAR - and matches it to a plain-language vision category.

The formulas

Every output comes from the same fraction, with numerator N and denominator D:

  • Decimal acuity = N / D. 20/20 = 1.0, 20/40 = 0.5, 20/200 = 0.1. Higher is sharper.
  • MAR (arcminutes) = D / N. The smallest detail you can resolve, expressed as an angle. 20/20 = 1 arcminute; 20/40 = 2 arcminutes.
  • LogMAR = log10(D / N). The base-10 logarithm of MAR. 20/20 = 0.00, 20/40 is about 0.30, 20/200 = 1.00. Lower is sharper, and better-than-normal acuity (20/15, 20/10) gives a negative LogMAR.

Because the outputs depend only on the ratio, a metric result reads the same way: 6/12 gives the identical decimal (0.5), MAR (2), and LogMAR (about 0.30) as 20/40.

Reading the vision category

20/20 or sharper is normal acuity. 20/25 to 20/40 is near-normal - 20/40 is the vision standard for an unrestricted driver license in most US states. Worse than 20/40 up to 20/200 is treated as low vision, and 20/200 or worse in the better eye with best correction meets the US definition of legal blindness. These bands are general reference points, not clinical grades.

When to consult a professional

This tool converts an acuity fraction you already have; it does not test your eyesight or diagnose any condition. Screen size, lighting, and viewing distance all affect a self-administered chart. For an accurate measurement or any concern about your vision, see a licensed optometrist or ophthalmologist.

Frequently Asked Questions

What does 20/20 vision actually mean?
20/20 means that at 20 feet you can read the line an average person reads at 20 feet - a minimum angle of resolution of 1 arcminute (LogMAR 0). It is defined as normal reference acuity, not perfect or maximum vision; many healthy eyes see 20/15 or even 20/10.
How do I convert 20/40 to decimal and LogMAR?
Decimal acuity is the fraction itself: 20/40 = 0.5. MAR is the denominator over the numerator: 40/20 = 2 arcminutes. LogMAR is log10 of the MAR: log10(2) is about 0.30. So 20/40 vision is decimal 0.5, MAR 2, LogMAR 0.30.
What is the minimum angle of resolution (MAR)?
MAR is the smallest angular gap your eye can distinguish, in arcminutes (1/60 of a degree). Normal 20/20 vision resolves 1 arcminute. MAR equals the Snellen denominator divided by the numerator, so a larger MAR means blurrier vision; LogMAR is simply its base-10 logarithm.
Is 20/15 better than 20/20?
Yes. 20/15 means you can read at 20 feet what an average person only reads at 15 feet, so your acuity is sharper than the 20/20 reference. Its decimal acuity is about 1.33, its MAR is 0.75 arcminutes, and its LogMAR is negative (about -0.12).

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