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Visual Acuity

20/20, 6/6, decimal, logMAR — notation only

Letter charts write the same line in more than one way. Type any one of US 20/x, metre 6/x, decimal, or logMAR and the others fill in. This is arithmetic on the notation, not a test of your eyes. There is no chart to read on this page.

How this works: decimal = 20 ÷ US denominator = 6 ÷ metre denominator. logMAR = −log10(decimal). So 20/40 = 6/12 = 0.5 = logMAR 0.3. 20/20 (6/6, decimal 1.0, logMAR 0.0) is typical chart normal, not “perfect” sight. Contact-lens versus glasses power (vertex distance) is not converted here, and this page has no sphere, cylinder, or axis engine.

Type in one box. Accepts 20/40, 40, 6/12, 0.5, or 0.3.

20/20
US Snellen
6/6
Metre Snellen
1.00
Decimal
0.00
logMAR

Sight-type words (not a diagnosis)

MyopiaNear objects look clearer than distant ones. Often called short-sight. A word for a refractive pattern, not a test result from this page.
HyperopiaDistant objects are often easier than near ones. Often called long-sight. Same caveat: a label, not a reading here.
AstigmatismBlur that can change with the direction of a line — a football-shaped front surface is the usual classroom picture.
PresbyopiaNear focus gets harder with age as the lens inside the eye stiffens. Common after the mid-forties. Not a chart score.

Same line, four writings

USMetreDecimallogMAR
Notation only — not an eye test. This page does not measure vision, write a prescription, or diagnose anything. A phone or printed chart is not a clinic. 20/20 is typical chart normal, not perfect. MultiSwitch is not optometry or medical advice — see Terms.

FAQ

What does a result like "20/40" or "6/12" actually mean?

The first number is the standard testing distance (20 feet or 6 metres). The second is the distance a person with standard vision could read the same line from — so 20/40 means you need to stand at 20 feet to read what a standard-vision person can read from 40 feet.

What's the difference between decimal and logMAR notation?

Decimal acuity is a straightforward ratio (20/20 = 1.0, 20/40 = 0.5). LogMAR is the logarithm of that ratio's reciprocal, used because it scales more evenly for research and statistics — with logMAR, a lower number means better vision, the reverse of decimal.

Is 20/20 "perfect" vision?

No — it's just the traditional reference line on a standard chart, not a ceiling. Many people test better than 20/20 (for example 20/15), and 20/20 says nothing about other aspects of vision like color, depth or peripheral sight.

Can this calculator convert my glasses or contact lens prescription?

No — it only converts between acuity notations (US, metric, decimal, logMAR). It doesn't handle sphere, cylinder, axis, or the vertex-distance adjustment between glasses and contact lens powers.

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