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What does your visual acuity mean in other notations?

Convert a visual acuity between Snellen feet (20/20), Snellen meters (6/6), decimal, logMAR and French tenths, and see how it compares with driving and low-vision thresholds.

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Decimal acuity

0.5

20/40 or better: meets the usual driving standard in most US states
French tenths (Monoyer)
5 /10
Snellen in feet: 20/…
40
Snellen in meters: 6/…
12
logMAR
0.301

This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.

Notations of visual acuity

Visual acuity measures the smallest detail you can see at a distance. The same result can be written in several ways:

  • Snellen in feet (20/x): used in the US. 20/40 means you see at 20 feet what a person with normal vision sees at 40 feet.
  • Snellen in meters (6/x): used in the UK, Australia and elsewhere. 6/12 equals 20/40.
  • Decimal: the fraction worked out, 20/40 = 0.5.
  • logMAR: the logarithm of the minimum angle of resolution, used in research and on ETDRS charts. 0 is normal, higher values are worse, and each line on the chart is 0.1.
  • Tenths (Monoyer scale): used in France. 10/10 equals a decimal of 1.0 and 5/10 equals 0.5.

Conversion formulas

Decimal = 20 ÷ x (feet) = 6 ÷ x (meters) = tenths ÷ 10

logMAR = −log₁₀(decimal)

Equivalence table

Feet Meters Decimal logMAR Tenths
20/20 6/6 1.0 0.0 10/10
20/25 6/7.5 0.8 0.1 8/10
20/40 6/12 0.5 0.3 5/10
20/63 6/19 0.32 0.5 3.2/10
20/100 6/30 0.2 0.7 2/10
20/200 6/60 0.1 1.0 1/10
20/400 6/120 0.05 1.3 0.5/10

Thresholds that matter in the US

  • Driving: most states require 20/40 or better in the better eye, with glasses or contacts if needed, for an unrestricted license.
  • Legal blindness: 20/200 or worse in the better eye with the best correction, or a visual field of 20 degrees or less.
  • WHO categories: moderate visual impairment is worse than 6/18 (about 20/60), severe worse than 6/60 (20/200) and blindness worse than 3/60 (20/400).

Example

A result of 20/40 equals 6/12, a decimal of 0.5, logMAR 0.3 and 5/10 on a French chart.

Limits

Visual acuity is only one part of vision. Contrast sensitivity, visual field, glare and night vision also matter. An eye care professional measures acuity under standard lighting and distance; a quick home test is not a substitute for an eye exam.

Frequently asked questions

What is 20/20 vision in decimal?

20/20 equals 1.0 in decimal, 6/6 in meters, logMAR 0 and 10/10 on the French Monoyer scale.

What does 20/40 mean?

You see at 20 feet what a person with normal vision sees at 40 feet. It equals 0.5 decimal and logMAR 0.3, and it is the usual minimum to drive without restrictions in most US states.

What visual acuity is legal blindness?

In the US, 20/200 or worse in the better eye with the best possible correction, or a visual field of 20 degrees or less.

How do I convert Snellen to logMAR?

Divide 20 by the denominator to get the decimal value, then take minus the base-10 logarithm. 20/100 is 0.2 decimal, or logMAR 0.7.

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Results are estimates provided for information purposes. They do not replace professional advice.

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