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October 31, 2026
The Snellen eye chart is read from 20 feet (6 meters) because its letters are sized for that distance and the eye barely has to focus there [1,2]. In a score like 20/40, you read at 20 feet what a person with standard vision can read at 40 feet [1]. 20/20 is standard vision, not perfect vision, and a chart score measures only one part of how well you see [3].
This article explains how eye charts work. It does not include a printable chart, and reading a chart at home is not an eye exam.
Key takeaways
In this article
A chart score changes slowly. Some vision changes happen suddenly and need care now, whatever your last chart result was.
See Netra’s guide to urgent vision changes for more warning signs.
The Snellen chart is read at 20 feet (6 meters) because the letters are sized for that distance and because the eye barely has to focus there. Light from 20 feet away reaches the eye almost parallel. So the test measures how sharply the eye sees at rest, not how hard it can strain to focus [2,13].
Herman Snellen, a Dutch eye doctor, designed the chart in 1862. It is still the most widely used acuity test in clinics [14].
Each Snellen letter is drawn on a five-by-five grid. At the test distance, a 20/20 letter is five minutes of arc tall, and each stroke and gap is one minute of arc. A minute of arc is one-sixtieth of a degree [15]. A person with standard 20/20 vision can tell apart two points one minute of arc apart [16]. Bigger lines use the same design scaled up, so a 20/200 letter is ten times as tall as a 20/20 letter.
The closer a chart is, the more the eye has to focus to see it. The focusing demand is about 0.33 diopters at 3 meters (10 feet) but only 0.11 diopters at 9 meters. Researchers use a fixed 6-meter distance so the demand is the same for everyone tested [2]. At 20 feet the demand is about one-sixth of a diopter, small enough that the eye is almost at rest.
A chart used at a shorter distance must have smaller letters to match. One research team added a +1.00 lens so that a chart 1 meter away acted like a distant one [13]. Charts with an even, logarithmic size scale make these distance adjustments simpler [4]. MedlinePlus notes that special charts are used when testing at less than 20 feet, and that some charts are video screens [1].
20/20 vision means that at 20 feet you can read the line that a person with standard vision reads at 20 feet. It is written 6/6 in meters. It is the usual benchmark for normal vision, but not perfect vision. Many adults see better, and acuity does not measure side vision, depth or color [1,3,16].
The fraction is a comparison, not a percentage. In 20/40, you see at 20 feet what a person with standard vision sees at 40 feet [1]. Each eye is tested on its own, first without glasses (uncorrected) and then with them, or with the best possible lenses (best corrected) [1]. You are still scored at a line if you miss one or two of its letters [1].
Scores better than 20/20, such as 20/15 or 20/10, are common. The average acuity in adults aged 18 to 80 may be better than 20/20, and it tends to be sharpest between ages 25 and 29 [16].
Each score tells you how much larger a letter must be for you to read it, compared with standard vision. At 20/40 you need letters twice as large as standard, and at 20/200 ten times as large. On the standard ETDRS research chart, the top line is 1.0 LogMAR, which equals 20/200 [13].
The table shows common scores in feet, meters and LogMAR.
| US score (feet) | Metric score (meters) | LogMAR | What it means |
|---|---|---|---|
| 20/10 | 6/3 | −0.3 | Twice as sharp as standard |
| 20/15 | 6/4.5 | −0.1 | Better than standard; common in young adults |
| 20/20 | 6/6 | 0.0 | Standard vision |
| 20/30 | 6/9 | 0.2 | Slight blur; not counted as vision impairment |
| 20/40 | 6/12 | 0.3 | Federal minimum for commercial drivers, in each eye with or without glasses |
| 20/60 | 6/18 | 0.5 | Worse than 20/40 to 20/60 is mild vision impairment |
| 20/70 to 20/400 | 6/21 to 6/120 | 0.5 to 1.3 | Moderate to severe vision impairment |
| 20/200 | 6/60 | 1.0 | US legal blindness line, if best corrected in the better eye |
| Worse than 20/400 | Worse than 3/60 | Above 1.3 | Blindness in global (GBD) studies |
Sources for the table: impairment levels from the Global Burden of Disease study [17]; driver standard from federal rules [18]; legal blindness from Social Security rules [5]. LogMAR values are rounded.
The commercial driver rule requires at least 20/40 in each eye and in both eyes together, with or without glasses. It also requires a side-to-side field of at least 70 degrees in each eye, with an alternative standard for some drivers [18]. Rules for ordinary driver’s licenses are set by each state and vary [19].
A score of 20/200 means you must be 20 feet away to read what a standard eye reads at 200 feet. It counts toward legal blindness only when it is your best-corrected vision in your better eye [5]. Someone who sees only the top letter without glasses but 20/20 with them is not legally blind. Netra’s guide to what legally blind means in the US covers the rules in detail.
LogMAR stands for the logarithm of the minimum angle of resolution, the smallest detail an eye can see. On this scale 0.0 equals 20/20, and higher numbers mean worse vision. Each line on a LogMAR chart is a step of 0.1, so 20/40 is 0.3 and 20/200 is 1.0 [3,13,16].
The Snellen chart has uneven jumps between lines and a different number of letters on each line. LogMAR charts fix this. The ETDRS chart, used in most research, has five letters of equal difficulty on every line. Letter size shrinks by the same ratio from line to line [4,6]. Because every letter counts, small changes can be measured.
The two charts do not always agree. In 237 patients tested on both charts on the same day, Snellen scores were slightly better on average. The gap went in different directions for poor and good vision [20]. One reviewer has argued that Snellen charts are not precise enough for accurate clinical or research measurement [21]. In practice, a one-line change between two visits on different charts may not be a real change [8,20].
When someone cannot read the largest letter, the examiner holds up fingers and records the distance at which the person can count them correctly [1]. Below that come hand motion, light perception and no light perception. Together these form a rough scale for very low vision that can be recorded and followed over time [7].
Researchers have measured what these levels mean using a computer test with very large symbols. Counting fingers at 30 cm came out at about 20/1,400 in one study and about 20/2,000 in another, and hand motion at about 20/4,000. Light perception could not be measured any further [7,22].
The worst level of vision is no light perception, meaning total blindness in that eye. Most people described as blind still have some sight. In global studies, blindness means vision worse than 3/60 (about 20/400) or a visual field narrower than 10 degrees around the center [17].
By that measure, about 43 million people worldwide were blind in 2020, and about 295 million had moderate or severe vision impairment [17]. The leading causes of vision impairment and blindness are refractive errors and cataract, both treatable [23]. A poor chart score is a reason for an exam, not a final verdict.
When vision loss makes daily tasks hard and cannot be fixed with glasses, contact lenses, medicine or surgery, it is called low vision. Treatment includes vision aids and vision rehabilitation [24]. See Netra’s guide to low-vision tools and rehabilitation.
A letter chart measures one thing: how sharp central vision is at high contrast. It does not test side vision, depth perception or color vision [3]. Glaucoma, for example, usually has no early symptoms and tends to take side vision first. It is found with a dilated exam and a visual field test, not a chart [11]. Netra’s guide to glaucoma tests explains those checks.
Contrast matters too. A review of driving standards found that good contrast sensitivity is at least as important as good acuity for safe driving [19].
You can screen your vision at home, but a home score is not an eye exam. Some home and smartphone tests come close to office results when used carefully. Still, no chart can tell you why your vision is blurry, and a new or uneven change needs a full exam [1,8].
A systematic review of 14 studies found that the best-studied smartphone app scored within about half a line of the clinic ETDRS chart on average [8]. Even clinic charts give slightly different results from one test to the next [8].
We have chosen not to offer a printable chart. A chart printed at home is rarely the right size for the distance you use. If size and distance do not match, the fraction you read is not a true score. Lighting, screen scaling, squinting and memorizing the letters all change the result.
Most of all, a chart shows how blurred the letters are, not why. Blur can come from a refractive error that glasses can fix or from an eye condition that needs care [1]. Telling them apart takes a comprehensive eye exam, which often includes dilating drops [25]. Netra’s guide to how often to have an eye exam explains what a visit includes. Our guide to blurry vision causes covers what you can and cannot fix at home. Children need professional vision screening, because untreated problems can cause lasting vision loss [1]; see our guide to children’s vision exams.
Netra Eye Institute does not diagnose or treat eye disease as an ophthalmologist would, and does not prescribe eye medicines [26]. Netra Restoration Therapy (NRT) is adjunctive care, used alongside the diagnosis, monitoring and treatment your eye doctor provides, never instead of them [27]. NRT has not been tested in controlled trials for improving visual acuity or for refractive errors such as myopia.
The acuity your eye doctor measures, under standard conditions, is the number that counts. If you are considering NRT, keep your glasses, treatment and follow-up in place, and bring your recent eye exam reports. See NRT effectiveness by diagnosis for how Netra reviews outcomes.
A standard eye chart is read from 20 feet, or 6 meters. Charts made for shorter rooms use smaller letters sized for that distance. A score is only accurate when the chart’s letter size matches the distance you stand from it.
A Snellen chart is the standard eye chart of letters that get smaller line by line, first designed by Dutch eye doctor Herman Snellen in 1862. It is read one eye at a time from 20 feet. The smallest line you can read gives your visual acuity score, such as 20/20.
20/40 vision is mild blur, not a serious level of vision loss. It means you see at 20 feet what a person with standard vision sees at 40 feet. It meets the federal minimum for commercial drivers, but an eye exam can show whether glasses or contacts would sharpen it.
20/30 vision is slightly below standard but still good. It is not counted as vision impairment in global studies, which start at vision worse than 20/40. An eye exam can show whether glasses would make it sharper.
Scores such as 20/15 and 20/10 are better than 20/20. 20/15 means you can read at 20 feet what a standard eye reads at 15 feet. Many healthy young adults see better than 20/20.
20/70 vision means you need letters three and a half times larger than standard to read them. In global studies it counts as moderate vision impairment. If 20/70 is your best vision with glasses, ask your eye doctor about low-vision aids.
20/200 vision means you must be 20 feet away to read what a person with standard vision can read from 200 feet. On many charts, including the standard research chart, this is the top line. In the US, 20/200 or worse in the better eye, with the best glasses or contacts, is the legal blindness line.
You can screen your vision at home, but it is not an eye exam. A printed chart is often the wrong size for your distance, which makes the score inaccurate. A home test also cannot tell why vision is blurry, so any new change needs a professional exam.
Sources checked October 31, 2026.
This article provides general education and does not replace an individual eye examination, diagnosis or treatment plan. If your vision drops suddenly, or you see new floaters, flashes or a curtain over your vision, get emergency eye care right away instead of testing your vision at home.
