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Visual Acuity Converter

Convert visual acuity between Snellen 20/x and 6/x, decimal, MAR and logMAR, and see its WHO ICD-11 category. It converts a reading; it is not an eye test. How it works

Use the Visual Acuity Converter

Examples: 20/40, 6/12, 20/25-1, 0.5, logMAR 0.3, CF, HM, LP, NLP

WHO ICD-11 category
Category 0

This page does not test your eyes. It converts an acuity value you type, taken from a chart reading someone else measured, between Snellen, decimal, MAR and logMAR. To have your vision measured, see an eye care professional.

The same acuity in other units

Decimal acuity
1
Snellen (feet)
20/20
Snellen (metres)
6/6
MAR
1 arcmin
logMAR
0.00

In the WHO ICD-11 distance-acuity table this value is equal to or better than 6/12 (20/40) (category 0, listed as no vision impairment).

The WHO classification this table follows is described, in the BMC Medicine article that proposes it, as based on presenting distance acuity in the better eye. One typed number cannot show which eye it is, whether glasses or contacts were worn, or how it was measured, and acuity is only one part of eye health. A band is not a diagnosis.

WHO ICD-11 vision impairment table (distance acuity, better eye)

Categories of vision impairment by presenting distance visual acuity. Each limit is given as metric Snellen, feet Snellen, decimal and logMAR.
CategoryWorse thanEqual to or better than
0 No vision impairmentYour value is in this rownone6/12 | 20/40 | decimal 0.5 | logMAR 0.3
1 Mild vision impairment6/12 | 20/40 | 0.5 | 0.36/18 | 20/60 (the table prints 20/70) | 0.333 (printed 0.3) | 0.5
2 Moderate vision impairment6/18 | 20/60 (the table prints 20/70) | 0.333 (printed 0.3) | 0.56/60 | 20/200 | 0.1 | 1.0
3 Severe vision impairment6/60 | 20/200 | 0.1 | 1.03/60 | 20/400 | 0.05 | 1.3
4 Blindness3/60 | 20/400 | 0.05 | 1.31/60 or counting fingers at 1 metre | 20/1200 | 0.0167 (printed 0.02) | 1.8
5 Blindness1/60 | 20/1200 | 0.0167 (printed 0.02) | 1.8light perception
6 Blindnessnoneno light perception

Each limit reads metric Snellen | feet Snellen | decimal | logMAR. The metric limit is the definition: 6/18 is exactly 20/60 and decimal 0.333, and the decimal, feet and logMAR columns of the published table are rounded prints of it (20/70, 0.3, logMAR 0.5). This page compares a typed Snellen value with the exact metric limit, a typed decimal with the limit rounded to three digits, and a typed logMAR value with the table's own logMAR column. The 6/18, 6/60, 3/60 and 1/60 limits match Table 1 of BMC Medicine 2006 (PMC1435919), which reproduces the WHO ICD-10 table; that table has no 6/12 row and no logMAR column, so the 6/12 limit and the category names come from Table 3 of the same article (a proposal by its authors) and from the ICD-11 mirror; the ICD-11 logMAR column here comes from a mirror of the table (findacode.com) because WHO's own ICD-11 page could not be opened, so treat the logMAR column as unverified against WHO.

MAR is 1 divided by decimal acuity, in arcminutes; logMAR is the base-10 logarithm of MAR.

Sudden loss or change of vision, new flashes of light, a shower of new floaters, a curtain or shadow across your vision, or eye pain with vision loss needs urgent care: contact an eye doctor or emergency service now rather than waiting for an appointment.

This is general information only. Consult a licensed eye care professional (optometrist or ophthalmologist) about your eyes.

About the Visual Acuity Converter

20/20 = 6/6 = decimal 1 = MAR 1 arcmin = logMAR 0.00, and 20/40 = 6/12 = decimal 0.5 = MAR 2 arcmin = logMAR 0.30. Decimal acuity is the value of the Snellen fraction, MAR is 1 divided by it, and logMAR is the base-10 logarithm of MAR. The converter also shows which row of the WHO ICD-11 distance-acuity table a typed value falls in; it does not test your eyes.

Snellen 20/x conversion chart

Snellen (feet)Snellen (metres)DecimalMARlogMARICD-11 category
20/2006/600.110 arcmin1.002: moderate vision impairment
20/1006/300.25 arcmin0.702: moderate vision impairment
20/806/240.254 arcmin0.602: moderate vision impairment
20/706/210.2863.5 arcmin0.542: moderate vision impairment
20/606/180.3333 arcmin0.481: mild vision impairment
20/506/150.42.5 arcmin0.401: mild vision impairment
20/406/120.52 arcmin0.300: no vision impairment
20/306/90.6671.5 arcmin0.180: no vision impairment
20/256/7.50.81.25 arcmin0.100: no vision impairment
20/206/611 arcmin0.000: no vision impairment
20/156/4.51.330.75 arcmin-0.120: no vision impairment
20/106/320.5 arcmin-0.300: no vision impairment

Each row is what the converter shows for the 20/x value typed. The category is the row of the ICD-11 distance-acuity table and is not a diagnosis.

Metric Snellen 6/x conversion chart

Snellen (metres)Snellen (feet)DecimalMARlogMARICD-11 category
6/6020/2000.110 arcmin1.002: moderate vision impairment
6/3620/1200.1676 arcmin0.782: moderate vision impairment
6/2420/800.254 arcmin0.602: moderate vision impairment
6/1820/600.3333 arcmin0.481: mild vision impairment
6/1220/400.52 arcmin0.300: no vision impairment
6/920/300.6671.5 arcmin0.180: no vision impairment
6/7.520/250.81.25 arcmin0.100: no vision impairment
6/620/2011 arcmin0.000: no vision impairment

Each row is what the converter shows for the 6/x value typed.

WHO ICD-11 categories of distance vision impairment

CategoryWorse thanEqual to or better than
0 No vision impairmentnone6/12 | 20/40 | decimal 0.5 | logMAR 0.3
1 Mild vision impairment6/12 | 20/40 | 0.5 | 0.36/18 | 20/60 (the table prints 20/70) | 0.333 (printed 0.3) | 0.5
2 Moderate vision impairment6/18 | 20/60 (the table prints 20/70) | 0.333 (printed 0.3) | 0.56/60 | 20/200 | 0.1 | 1.0
3 Severe vision impairment6/60 | 20/200 | 0.1 | 1.03/60 | 20/400 | 0.05 | 1.3
4 Blindness3/60 | 20/400 | 0.05 | 1.31/60 or counting fingers at 1 metre | 20/1200 | 0.0167 (printed 0.02) | 1.8
5 Blindness1/60 | 20/1200 | 0.0167 (printed 0.02) | 1.8light perception
6 Blindnessnoneno light perception

Each limit reads metric Snellen | feet Snellen | decimal | logMAR. The metric limits are the ones in BMC Medicine 2006 (Table 3, which proposed the mild category and the use of presenting acuity). The logMAR column is taken from a third-party copy of the ICD-11 table (findacode.com) and has not been compared with WHO's own ICD-11 browser.

Frequently asked questions

What is 20/40 vision in decimal and logMAR?
Decimal 0.5 and logMAR 0.30; in metres it is 6/12 and the MAR is 2 arcmin. 20/40 is the limit of category 0 in the ICD-11 table: equal to or better than 6/12 is listed as no vision impairment.
Is 20/70 the same as 6/18?
No. 6/18 is exactly 20/60 (decimal 0.333, logMAR 0.48); 20/70 is 6/21 (decimal 0.286, logMAR 0.54). The published table prints the 6/18 limit as 20/70 and 0.3, rounded. The converter compares a Snellen fraction with the exact metric limit, so 20/60 falls in category 1 (mild) and 20/70 in category 2 (moderate).
How do I convert Snellen to logMAR?
Divide the top number by the bottom one to get decimal acuity, take 1 divided by that for MAR, and take the base-10 logarithm of MAR. For 20/80: 20 ÷ 80 = 0.25, MAR 4 arcmin, logMAR 0.60.
What does 20/25-1 mean?
The -1 records letters missed on, or read beyond, the 20/25 line. The converter notes the modifier and does not use it, so 20/25-1 converts as 20/25: decimal 0.8, 6/7.5, logMAR 0.10.
Why is a typed 0.3 in a different category from 6/18?
A typed decimal is compared with the limit rounded to three digits, 0.333, so 0.333 is category 1 and 0.3 (6/20) is category 2. A typed logMAR value is compared with the table's own rounded logMAR column: logMAR 0.5 is category 1 and 0.51 is category 2.
How do I enter a logMAR value or a code like CF?
Type the word with the number, as logMAR 0.3 or 0.3 logMAR. That gives 6/12 and decimal 0.501. A bare 0.3 is read as decimal acuity instead, which is 6/20 and logMAR 0.52, a different line. CF, HM, LP and NLP are accepted and explained, but get no figures, since they are not chart lines.

Snellen, decimal and logMAR: what each scale is for

20/40 and 6/12 are the same reading, one in feet and one in metres: you read at 20 feet (6 m) the line a reference eye reads at 40 feet (12 m). Decimal acuity is that fraction worked out, 0.5. logMAR rises by 0.1 for each line lost on a logMAR chart, so it is the scale to use when you average readings or compare two visits. Type a value as 20/40, 6/12, 0.5 or logMAR 0.3.

The conversions and the categories

decimal = numerator ÷ denominator, MAR = 1 ÷ decimal in arcminutes, and logMAR = log10(MAR) = −log10(decimal). Example: 20/80 gives decimal 0.25, 6/24, MAR 4 arcmin and logMAR 0.60. A modifier such as the -1 in 20/25-1 is noted and not used.

The WHO ICD-11 category compares the value with the limits 6/12, 6/18, 6/60, 3/60 and 1/60:

  • a Snellen value exactly: 6/18 is 20/60, category 1, while 20/70 is 6/21, category 2

  • a typed decimal against the limit rounded to three digits: 0.333 is category 1, 0.3 is category 2

  • a logMAR value against the table's own rounded logMAR column: 0.5 is category 1, 0.51 is category 2

Accepted range: 20/6.3 to 20/2000, decimal 3.17 to 0.01, logMAR -0.5 to 2.0. A category is not a diagnosis.

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