What is the required distance an adult must stand from a Snellen chart for a visual acuity test?

• A. 10 feet
• B. 20 feet
• C. 20 meters
• D. 10 meters

Answer: (B)

The test distance is standardized so the letter sizes on the chart align with a person’s true visual acuity. A Snellen chart is designed so that 20/20 vision means you can read the letters at 20 feet what a person with normal vision can read at that distance. That fixed distance keeps results consistent and interpretable. Standing at 20 feet (about 6 meters) ensures the line sizes correspond to the acuity ratings correctly; moving closer would make letters look larger and falsely improve measured acuity, while standing farther would make them look smaller and lower the result. The other distances don’t match the chart’s calibration (20 meters is far beyond typical use, and 10 feet or 10 meters don’t correspond to the standard 20/20 sizing).