Reading glasses come in strengths from +1.00 to +3.50 diopters, increasing in +0.25 steps, and the right one for you depends mostly on your age and how close you hold what you’re reading. You can narrow it down with a simple age-based guide, then confirm your choice by testing a few pairs in a store or using a printable eye chart at home.
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 far and near objects. This process, called presbyopia, is universal. It doesn’t matter whether you’ve had perfect vision your whole life. It progresses steadily until your mid-60s, when the lens has lost most of its flexibility.
The earliest signs are subtle: needing more light to read, holding your phone or a menu farther from your face, or getting headaches after close-up work. If you notice blurred vision at a normal reading distance or your eyes feel sore and tired after reading for a while, those are classic signals that it’s time to pick up a pair of readers.
What the Numbers on Reading Glasses Mean
The “+” number on a pair of reading glasses is measured in diopters, a unit of magnifying power. A +1.00 pair provides the least magnification, suited for mild difficulty with fine print. A +3.50 pair is the strongest commonly available and brings very close objects into sharp focus. Each +0.25 step up adds a small but noticeable bump in magnification.
Higher is not better. Choosing a strength that’s too powerful forces your eyes to work against the extra magnification, which causes headaches and fatigue, the same symptoms you’re trying to fix. The goal is always the lowest strength that makes text clear and comfortable.
Age-Based Starting Points
Your age gives you the best first estimate. Presbyopia follows a remarkably predictable curve:
- Ages 40 to 45: +0.75 to +1.25 diopters
- Ages 46 to 50: +1.25 to +1.50 diopters
- Ages 51 to 55: +1.50 to +2.00 diopters
- Ages 56 to 60+: +2.00 to +2.50 diopters
These ranges assume you’re reading a book or phone held about 14 to 16 inches from your face. If you already wear glasses or contacts for distance vision, these numbers won’t apply directly because your existing prescription changes the math. In that case, an eye exam is the more reliable route.
How to Test at Home
Several eye care departments and universities publish free printable near-vision charts online. The University of Arizona’s ophthalmology department, for example, offers one designed for home use. The key steps are straightforward: print the chart at full size (100% scale, not “fit to page”), hold it exactly 14 inches from your eyes, and read the smallest line you can see clearly. The diagonal of a standard sheet of paper is about 14 inches, so you can use that as a built-in ruler.
Before you trust your results, verify the chart printed at the correct size. Most charts include a reference image of a quarter. Hold an actual quarter against it. If they don’t match, your printout is scaled incorrectly and the results will be off. Test each eye individually by covering the other, then test both eyes together. This also helps you spot a significant difference in strength between your two eyes, which is important information (more on that below).
How to Test in a Store
The reading glasses aisle at any pharmacy is essentially a free fitting room. Grab two or three pairs around the strength your age suggests and try reading actual material you brought with you: a book, your phone, a medication label. The test cards attached to store displays use large fonts that can make almost any strength seem fine, so real-world text is a better test.
If your home chart or age range pointed you toward +1.50, try +1.25, +1.50, and +1.75. Read at the distance you’d normally hold a book, not with your arms stretched out and not with the page against your nose. The pair that makes text crisp without any sense of effort or strain is your winner.
If two adjacent strengths both seem to work, go with the lower one. The weaker pair will cause less eye strain during long reading sessions. You can always step up by +0.25 a year or two later as presbyopia naturally progresses.
Computer Screens Need a Different Strength
Reading glasses are calibrated for book distance, roughly 14 to 16 inches. A computer monitor sits much farther away, typically 20 to 28 inches. If you use your full-strength readers at the computer, text may look magnified but your eyes will strain to focus at that intermediate distance.
The general rule is to subtract 0.50 to 1.00 diopters from your reading strength for comfortable screen use. If your monitor is on the closer end (20 to 24 inches), subtract about 0.50. If it’s farther out (24 to 28 inches), subtract 0.75 to 1.00. So if you wear +2.00 readers for books, a +1.25 or +1.50 pair will likely feel better at your desk. Many people keep two pairs for this reason: one for reading, one for the computer.
When Over-the-Counter Readers Won’t Work
Store-bought reading glasses have the same strength in both lenses. That’s their biggest limitation, because very few people have identical vision in both eyes. If one eye needs noticeably more help than the other, generic readers will feel slightly off no matter which strength you pick. Your stronger eye compensates for the weaker one, and the result is fatigue and headaches that don’t go away even after switching pairs.
Over-the-counter readers also only magnify. They do not correct astigmatism, which is a subtle warping of the cornea that blurs or distorts text at any distance. If letters look smeared, shadowed, or doubled rather than simply blurry, magnification alone won’t fix the problem. The same goes for nearsightedness or other refractive issues layered on top of presbyopia. In any of these cases, you need a prescription pair with lenses ground to match each eye independently.
A practical way to screen for this: during your home or in-store test, cover one eye and then the other. If one eye is clearly sharper than the other with the same pair of readers, or if no strength seems to fully clear up the text, that’s a strong signal to get a professional exam rather than continuing to guess.
Expect Your Strength to Change
Presbyopia is progressive. The pair that works perfectly at 45 will feel too weak by 50. Most people move up by about +0.25 to +0.50 diopters every few years through their 40s and 50s, with the progression leveling off in the early to mid-60s. When your current readers start forcing you to hold pages farther away again, it’s time to step up.
Because over-the-counter readers are inexpensive, there’s no reason to stick with a pair that no longer does the job. Re-test every couple of years using the same method you started with, whether that’s an age chart, a printable test, or a trip to the pharmacy aisle.