A printable Snellen chart is available on the free eye chart page of VisionSource.com, as of July 2015. The chart is available in PDF and JPEG formats.
Visit the VisionSource.com homepage, and place the cursor over Patients. Click on Free Eye Chart Download. Click on the eye chart image to open it as a PDF, or the Click Here link to open it as a JPEG.
Print the chart on 8 1/2-inch by 11-inch paper; make sure the size is correct to avoid inaccurate measurements. Set the chart up at your eye level in a room with ample lighting, on a wall without windows. Stand 10 feet from the chart, cover one eye and read the lowest line possible. The lowest line where you could identify a majority of the letters correctly is your visual acuity for that eye. Repeat the process to check the vision for your other eye.
Each line on the chart corresponds to a visual acuity. Visual acuity is measured according to what a person with standard vision can see from 20 feet away. For example, 20/40 vision means that the person sees things 20 feet away as well as someone with standard vision sees things 40 feet away. If a person's corrected vision is less than 20/200, he is considered to be legally blind in the United States. Although 20/20 is standard vision, it isn't perfect; it's possible for people to have a better visual acuity.