The strength of reading glasses you need depends on your age, how close you hold things to read, and whether your eyes have other issues like astigmatism. Most people start with a low power like +1.00 in their early 40s and gradually move up over time. You can narrow down your number with a simple at-home test, but understanding what the numbers mean and when they stop being useful will save you from headaches, wasted money, and blurry frustration.
Why You Need Them in the First Place
Starting around age 40, the lens inside your eye gradually stiffens and loses its ability to shift focus between distant and nearby objects. This is called presbyopia, and it happens to virtually everyone. The classic early signs: you catch yourself holding your phone or a menu farther away to sharpen the text, words blur at normal reading distance, or you get headaches after reading or close-up work. These symptoms tend to be worse when you’re tired or in dim lighting.
Presbyopia gets progressively stronger through your 40s, 50s, and into your 60s, which means the reading glass strength that works perfectly today will likely need an upgrade every few years.
What the Numbers on Reading Glasses Mean
Reading glasses are labeled with a “+” number that represents their magnifying power in units called diopters. A higher number means stronger magnification. Over-the-counter readers typically start at +1.00 and go up in 0.25 steps to about +3.25 or +3.75.
As a rough guide, people in their early 40s often land around +1.00 to +1.25, those in their late 40s to early 50s around +1.50 to +2.00, and people in their 60s may need +2.50 or higher. These are ballpark ranges. Your actual number depends on the specific condition of your eyes, not just your birthday.
How to Test Your Strength at Home
The quickest method is a printable diopter chart, like the free one from Foster Grant. Print it at 100% scale on paper (not on a screen, since screen brightness skews the results). Hold or hang the chart exactly 14 inches from your face without wearing any glasses. The chart shows lines of text in decreasing sizes, each labeled with a diopter value starting at +1.00 at the top. The first line you can read clearly tells you your approximate strength.
If you’d rather skip the printout, head to a drugstore and try on a few pairs. Start with the lowest power on the rack and read something with small text at a comfortable distance, around 14 to 16 inches. Move up in 0.25 increments until the text looks sharp without any effort. The right pair should make reading feel effortless. If you have to squint or lean in, you need more power. If the text looks magnified but slightly swimmy, you’ve gone too strong.
Computer Screens Need a Different Strength
Standard reading glasses are designed for a working distance of about 14 to 16 inches, the distance between your eyes and a book in your lap. A computer monitor sits much farther away, typically 20 to 26 inches. If you use your reading glasses for screen work, everything will look slightly blurry or you’ll find yourself hunching forward to get closer.
For computer use, reduce your reading power by about 0.50 to 0.75 diopters. So if you use +2.00 readers for books, try +1.25 to +1.50 for your monitor. Some people keep two pairs: one for reading and one for the desk. Progressive lenses are another option that handles both distances in a single pair, though those require a prescription.
Signs You Picked the Wrong Strength
The wrong power doesn’t just fail to help. It actively causes problems. Glasses that are too strong or too weak can trigger eye strain, burning or heavy-feeling eyes, and headaches concentrated around your forehead or temples. These symptoms typically show up after sustained reading or screen time rather than immediately.
More dramatically, a significantly wrong power can cause dizziness and nausea, especially during movement like walking down stairs, turning your head quickly, or navigating a grocery store aisle. Your brain relies on consistent visual signals to maintain balance, and distorted optics send conflicting information. If a new pair of readers makes you feel queasy or unsteady, take them off. You likely need a different strength, or you may have an issue that over-the-counter glasses can’t address.
When Drugstore Glasses Won’t Work
Over-the-counter readers have a fundamental limitation: both lenses are the same strength, and they only correct simple magnification. That works well if both of your eyes have roughly equal vision and no other optical issues. But many people don’t fit that profile.
If you have astigmatism, which is an irregularly shaped cornea, generic readers will make text bigger without actually making it clear. The directional blur from astigmatism requires a specific type of correction that off-the-shelf glasses simply can’t provide. Even a relatively mild astigmatism of 0.75 diopters or more almost always causes noticeable blur and discomfort that magnification alone won’t fix. Your brain and eyes end up working overtime to interpret a magnified but still-distorted image.
Over-the-counter readers also use a fixed optical center, meaning they assume your pupils are a standard distance apart. If your pupillary distance is significantly wider or narrower than average, the optical center of each lens won’t align with your eyes. This misalignment can cause the same headaches and dizziness as wearing the wrong strength.
Three situations call for a proper eye exam instead of the drugstore rack:
- You need different powers for each eye. If one eye is noticeably sharper than the other when you close them individually, generic readers will over-correct one eye and under-correct the other.
- You need a strength above +3.25. At that level, the chance of an underlying eye condition that needs professional evaluation goes up significantly.
- Drugstore readers never feel quite right. If you’ve tried multiple strengths and none of them give you comfortable, sharp vision, astigmatism or pupillary distance mismatch is the likely culprit.
Expect Your Needs to Change
Whatever strength works for you now, plan on it shifting. Most people move up by about +0.25 every two to three years through their 40s and 50s as the lens continues to stiffen. The progression generally levels off somewhere in the early to mid-60s. Repeating the at-home chart test or trying on new pairs at the store once a year is a simple way to stay ahead of the change rather than struggling with a pair that quietly became too weak six months ago.