What is 20/20 vision in logMAR?

20/20 visual acuity corresponds to approximately 0.00 logMAR.

What is 20/40 vision in logMAR?

20/40 visual acuity corresponds to approximately 0.30 logMAR.

How do you convert Snellen acuity to logMAR?

logMAR is calculated as log10 of the Snellen denominator divided by the Snellen numerator. For 20-foot Snellen notation, logMAR = log10(denominator / 20).

Is a lower logMAR score better?

Generally, lower logMAR values represent better visual acuity. A logMAR value of 0.00 corresponds to approximately 20/20, while negative values represent acuity better than the 20/20 reference.

Visual Acuity Reference

Snellen to logMAR Visual Acuity Conversion Chart

Compare Snellen visual acuity, logMAR and decimal acuity notation using the chart and calculator below. The normal reference of 20/20 corresponds to approximately 0.00 logMAR and decimal acuity 1.00.

Snellen to logMAR Calculator

Enter a Snellen numerator and denominator. In the United States, the numerator is usually 20.

Snellen numerator

Snellen denominator

20/40 is approximately 0.30 logMAR and 0.50 decimal acuity.

Visual Acuity Conversion Chart

The following table shows commonly used approximate equivalents between Snellen, logMAR and decimal acuity.

Snellen	logMAR	Decimal acuity
20/400	1.30	0.05
20/320	1.20	0.06
20/250	1.10	0.08
20/200	1.00	0.10
20/160	0.90	0.13
20/125	0.80	0.16
20/100	0.70	0.20
20/80	0.60	0.25
20/63	0.50	0.32
20/50	0.40	0.40
20/40	0.30	0.50
20/32	0.20	0.63
20/25	0.10	0.80
20/20	0.00	1.00
20/16	-0.10	1.25
20/13	-0.20	1.54
20/10	-0.30	2.00
20/8	-0.40	2.50
20/6	about -0.52	3.33
20/5	about -0.60	4.00
20/4	about -0.70	5.00

Note: Some clinical charts use standardized logMAR steps and rounded Snellen equivalents. Therefore, a displayed Snellen value and its exact mathematical conversion may differ slightly because of rounding.

How to Convert Snellen to logMAR

The general mathematical relationship is:

logMAR = log10(Snellen denominator ÷ Snellen numerator)

For standard U.S. 20-foot Snellen notation:

logMAR = log10(denominator ÷ 20)

Example: 20/40

logMAR = log10(40 ÷ 20)
logMAR = log10(2)
logMAR ≈ 0.30

How to Convert logMAR to Snellen

For a 20-foot Snellen numerator, the approximate denominator can be calculated from logMAR using:

Snellen denominator = 20 × 10^logMAR

Example: logMAR 0.30

denominator = 20 × 10^0.30
denominator ≈ 40

Therefore: 0.30 logMAR ≈ 20/40

What Does logMAR Mean?

logMAR means logarithm of the Minimum Angle of Resolution .

Unlike Snellen notation, logMAR uses a logarithmic scale. This makes it useful for comparing changes in visual acuity across standardized chart levels.

0.00 logMAR corresponds approximately to 20/20.
Positive logMAR values generally represent reduced visual acuity compared with the 20/20 reference.
Negative logMAR values represent acuity better than the 20/20 reference.

Snellen vs logMAR vs Decimal Acuity

Snellen

Snellen notation is widely recognized in the United States and is commonly written as values such as 20/20, 20/40 or 20/100.

logMAR

logMAR expresses visual acuity on a logarithmic scale. Standardized research and clinical charts often use logMAR because each step can represent a more consistent change in visual acuity.

Decimal acuity

Decimal acuity is another way to express visual acuity. It can be calculated approximately by dividing the Snellen numerator by the denominator.

Decimal acuity = Snellen numerator ÷ Snellen denominator

For example:

20/40 = 20 ÷ 40 = 0.50 decimal acuity

Common Visual Acuity Examples

What is 20/20 in logMAR?

20/20 corresponds to approximately 0.00 logMAR.

What is 20/40 in logMAR?

20/40 corresponds to approximately 0.30 logMAR.

What is 20/50 in logMAR?

20/50 corresponds to approximately 0.40 logMAR.

What is 20/100 in logMAR?

20/100 corresponds to approximately 0.70 logMAR.

Is a lower logMAR value better?

Generally, yes. Lower logMAR values indicate better visual acuity. The 20/20 reference is approximately 0.00 logMAR, while values below zero correspond to acuity better than that reference.

About Online Visual Acuity Measurements

Visual acuity measured through a web browser can be affected by physical screen size, display scaling, browser zoom, viewing distance, lighting and device settings.

For this reason, values calculated or displayed by an online screening tool should not automatically be interpreted as a clinically calibrated measurement.

Important: PeekVision provides preliminary browser-based vision screening and educational information only. It does not diagnose eye disease, determine an eyeglass prescription or replace a comprehensive professional eye examination.

Related PeekVision Resources

Learn more about visual acuity and online vision screening: