What Does 20/20 Vision Mean?

"20/20" is the best-known number in eye care, and also one of the most misunderstood. It does not mean perfect eyes, it does not mean you never need glasses, and it says nothing about your glasses prescription. It describes one thing: how small a letter you can read at a distance. This guide explains what the fraction means, how it relates to the 6/6, decimal, 10/10 and logMAR notations used around the world, which values matter for driving, and what an online eye test can and cannot tell you.

What 20/20 actually means

The notation comes from the Dutch ophthalmologist Herman Snellen, who published his letter chart in 1862. The top number is your distance from the chart: 20 feet, about 6 metres. The bottom number is the distance at which a person with standard vision can read the same line.

• 20/20: at 20 feet you read the line a person with standard vision reads at 20 feet.
• 20/40: at 20 feet you need letters that a person with standard vision could already read from 40 feet. Your acuity is half the standard.
• 20/15: at 20 feet you read letters that a person with standard vision needs to come within 15 feet to read. That is better than 20/20.

On a standard chart, the letters on the 20/20 line are 5 minutes of arc tall and each stroke is 1 minute of arc thick. In plain terms, 20/20 means your eye can separate details about one sixtieth of a degree apart. The American Academy of Ophthalmology summarises it this way: a person with 20/20 vision sees what an average person sees on an eye chart from 20 feet away.

20/20, 6/6, 1.0 and 10/10 are the same thing

Different countries write the same result in different ways:

• Feet (US): 20/20.
• Metres (UK, Australia, India and others): 6/6, because 20 feet is about 6 metres.
• Decimal (much of Europe): 1.0, simply the fraction worked out (20 ÷ 20). The decimal notation is often credited to the French ophthalmologist Ferdinand Monoyer (1875).
• Tenths (Turkey, France and others): 10/10, the decimal value written in tenths. 0.5 is 5/10, 0.8 is 8/10.
• logMAR (research and clinical trials): 0.0. It is the logarithm of the minimum angle of resolution, so smaller is better and 20/20 sits at zero.

Visual acuity conversion table

The rows below follow the conversion table in the DICOM standard (PS3.17, section RR.2.4), with the tenths column added. Each step of 0.1 logMAR is one line on a modern chart.

Older charts also have 20/30 (6/9, decimal about 0.66) and 20/60 (6/18, about 0.33) lines, which sit between the rows above.

Is 20/20 perfect vision?

No. The American Academy of Ophthalmology says plainly that 20/20 vision is not perfect vision. Snellen chose it as a reference standard, and many healthy eyes do better. Elliott, Yang and Whitaker (1995) measured healthy eyes across adulthood and found that typical acuity is better than 6/6, declining only in older age groups, which is why their paper is subtitled "Seeing beyond 6/6".

20/20 also measures only sharpness for high-contrast black letters at a distance. It does not measure:

• near vision, which weakens for almost everyone from around their forties;
• contrast sensitivity, how well you see faint, low-contrast shapes in fog or at dusk, which our contrast sensitivity test checks;
• colour vision, which the colour blind test screens;
• your field of vision, eye coordination or depth perception;
• eye health: an acuity number is not an eye examination, and a good score does not rule out eye disease.

20/20 vision and your glasses prescription

Acuity and prescription are different measurements. Your prescription (for example −1.50 or +2.00) is the lens power in dioptres that corrects your focus. Acuity is how small you can read, with or without that correction. Many people who wear glasses see 20/20 with them and much worse without them. When a clinic writes your acuity, it usually notes whether it was measured uncorrected or with your glasses or contact lenses.

Blur that is stronger in one direction can come from astigmatism, which is part of the prescription, not of the acuity number. The astigmatism test is a quick screen for it.

Thresholds that matter: driving and visual impairment

• European Union: for a car or motorcycle licence (Group 1), you need at least 0.5 (20/40) with both eyes together, with glasses or contact lenses if needed. For lorries and buses (Group 2), at least 0.8 in the better eye and 0.1 in the worse eye. These rules come from Directive 2006/126/EC. Its successor, Directive (EU) 2025/2205, entered into force on 25 November 2025 and keeps the same acuity standards; member states have until 26 November 2029 to apply it.
• Turkey: the national regulation on drivers' health requirements says acuity is measured with a Snellen chart. For Group 1 (cars, motorcycles), neither eye may be below 0.1 and the acuity of both eyes added together must reach 1.0, with or without correction. For Group 2, the worse eye needs 0.6 and the better eye 0.8, or both eyes 0.7. Drivers with one seeing eye need 1.0 in that eye.
• United States: most states require 20/40 or better for an unrestricted licence, according to the American Academy of Ophthalmology. People whose best corrected vision is 20/200 or worse are considered legally blind.
• World Health Organization (ICD-11): distance vision worse than 6/12 (20/40) in the better eye counts as mild impairment, worse than 6/18 as moderate, worse than 6/60 as severe, and worse than 3/60 as blindness.

Rules change and have exceptions, so check with your licensing authority or an eye doctor before relying on any figure here.

Can an online eye test tell you if you have 20/20?

Roughly. Our online eye test first asks you to calibrate the screen with a bank card, then draws the Tumbling E at the exact angle for the distance you pick, in 0.1 logMAR steps from 1.0 (20/200) to −0.2 (20/12.5). It reports an approximate Snellen fraction and decimal value for each eye.

The result is an estimate. It depends on how carefully you matched the card and measured the distance, on your screen's brightness and pixels, and on not peeking or squinting. It uses one optotype and a short sequence, so chance plays a bigger role than with a full chart. It does not replace an eye exam and should not be used to check a child's eyes.

When to see an eye doctor

Book an eye exam if your acuity is below 0.5 (20/40) in either eye, if your two eyes differ by two lines or more, if you notice blur, headaches or eye strain, or if you have not had an exam for a year or two. Children need professional testing, because a lazy eye is easy to miss and must be treated early.

Get help the same day if your vision drops or blurs suddenly, if a curtain or shadow covers part of your view, if you see new flashes of light or a shower of new floaters, or if an eye is painful and red.

Sources

• Snellen, H. (1862). Probebuchstaben zur Bestimmung der Sehschärfe. Utrecht: Van de Weijer.
• American Academy of Ophthalmology. What does 20/20 vision mean? aao.org
• DICOM Standard, PS3.17, Annex RR.2.4: Traditional charts (visual acuity notation conversion). dicom.nema.org
• Elliott, D. B., Yang, K. C. H., & Whitaker, D. (1995). Visual acuity changes throughout adulthood in normal, healthy eyes: Seeing beyond 6/6. Optometry and Vision Science, 72(3), 186–191.
• Directive 2006/126/EC of the European Parliament and of the Council on driving licences (recast), Annex III. Official Journal of the European Union, L 403.
• European Council of Optometry and Optics (2025). Vision and eyesight provisions in the updated EU Driving Licences Directive 2025 (Directive (EU) 2025/2205). ecoo.info
• Sürücü Adayları ve Sürücülerde Aranacak Sağlık Şartları ile Muayenelerine Dair Yönetmelik, article 5 (amended in Resmî Gazete 29577, 29 December 2015). mevzuat.gov.tr
• World Health Organization. International Classification of Diseases, 11th Revision (ICD-11), 9D90 Vision impairment including blindness.

Frequently asked questions