Your vision “out of 20” is a fraction that compares how well you see at 20 feet to how well a person with normal eyesight sees. The baseline is 20/20, which means normal, average vision. If your number is higher than 20 on the bottom, your vision is worse than average. If it’s lower, your vision is sharper than average.
What the Two Numbers Mean
The top number is always 20. It represents the distance in feet between you and the eye chart during the test. The bottom number is the smallest line of letters you could read correctly. That bottom number tells you the distance at which a person with normal vision could read that same line.
So if your result is 20/40, you need to stand 20 feet away to read what someone with normal vision could read from 40 feet. If your result is 20/100, you see at 20 feet what a normally-sighted person sees at 100 feet. The larger the bottom number, the blurrier your uncorrected vision is.
Outside the United States, the same system uses meters instead of feet. The standard testing distance is 6 meters, so 20/20 in the U.S. is the same as 6/6 in countries that use the metric system.
Common Scores and What They Mean
Here’s how the most common results translate to everyday experience:
- 20/10 or 20/15: Better than normal. You can pick out fine details that most people miss. 20/10 is roughly the sharpest human vision possible, meaning you see at 20 feet what most people need to be 10 feet away to see.
- 20/20: Normal, average vision. This is the benchmark, not perfection.
- 20/40: Mildly reduced. This is the cutoff for an unrestricted driver’s license in nearly every U.S. state. If your vision is worse than 20/40 in your better eye (with glasses or contacts), most states require a restricted license or won’t issue one at all.
- 20/70 to 20/100: Moderate vision loss. Reading standard print and recognizing faces across a room becomes difficult without correction.
- 20/200 or worse: This is the legal definition of blindness in the United States when measured in your better eye with the best possible corrective lens. A person with 20/200 vision needs to be 20 feet from something that a normally-sighted person can see from 200 feet away.
Your Score Is Not Your Prescription
A common source of confusion: the 20/X number from an eye chart is not the same thing as an eyeglass or contact lens prescription. Your prescription is measured in diopters, which describe the lens strength needed to bend light correctly for your eye. Two people can both have 20/80 uncorrected vision but need completely different prescriptions because one is nearsighted, the other farsighted, and one has astigmatism on top of it.
There’s no clean formula to convert a 20/X score into a diopter prescription. Your eye doctor measures them separately because they answer different questions. The 20/X score tells you how well you see right now. The prescription tells the lab how to grind your lenses.
What It Doesn’t Measure
The eye chart tests one specific thing: how clearly you can distinguish small, high-contrast letters at a distance. That’s called distance acuity, and it’s only one piece of functional vision. Your eyes also handle close-up reading (near acuity, tested at about 14 to 16 inches), peripheral vision, depth perception, the ability to distinguish between similar shades of light and dark (contrast sensitivity), and color discrimination. You can score 20/20 on a Snellen chart and still struggle with night driving because of poor contrast sensitivity, or have trouble catching a ball because of weak depth perception.
If your eye doctor suspects problems beyond distance clarity, they’ll use additional instruments that test these other visual functions separately. A standard eye chart appointment won’t catch everything on its own.
What “Corrected” vs. “Uncorrected” Means
When your results are written down, they often specify whether you were wearing correction during the test. Uncorrected acuity is your natural vision without glasses or contacts. Corrected acuity, sometimes written as “best corrected visual acuity,” is what you achieve with your optimal prescription in place. The distinction matters because legal standards, like driving requirements and the definition of legal blindness, are based on your corrected score in your better eye. Your uncorrected score tells your doctor how much work the lenses need to do, but it’s the corrected score that determines what activities you can safely perform.