Over-the-counter reading glasses typically come in strengths ranging from +1.00 to +3.50 diopters, sold in +0.25 increments. Some brands start as low as +0.75, and a few go up to +3.75, but the most common range on store shelves is +1.00 to +3.00. The “plus” number refers to magnifying power, and higher numbers mean stronger magnification.
Available Strengths at a Glance
Walk into any drugstore or retail shop and you’ll find readers lined up in these increments: +1.00, +1.25, +1.50, +1.75, +2.00, +2.25, +2.50, +2.75, +3.00, +3.25, and sometimes +3.50 or +3.75. That 0.25 step between each pair matters. Jumping a full step (say, from +1.00 to +1.50) can make text look sharp but cause headaches because the magnification is slightly more than your eyes need.
If you need something weaker than +1.00 or stronger than +3.75, you’re outside the range of what’s sold over the counter. At that point, prescription reading lenses are the way to go.
What Strength You Likely Need by Age
The lens inside your eye gradually stiffens as you age, making it harder to focus on close-up text. This process, called presbyopia, is why almost everyone eventually needs readers. It usually becomes noticeable in your early to mid-40s and continues progressing into your 60s. General starting points by age:
- 40 to 45: +0.75 to +1.25
- 45 to 50: around +1.50
- 50 to 55: +1.75 to +2.00
- 55 to 60: +2.25 to +2.50
- 60 to 65: +2.75 to +3.25
- 65 and older: +3.25 and higher
These are averages. If you’re nearsighted, farsighted, or have astigmatism, your ideal strength could be quite different from what your age alone suggests. People who already wear distance glasses often need a different calculation entirely, because readers have to compensate for (or work alongside) an existing prescription.
How to Find Your Strength at Home
The simplest test is the printed diopter chart method. Several eyewear brands offer free downloadable charts you print at full size on paper (not read on a screen). Hold the chart 14 inches from your face without any glasses on and read from the top line down. The lines are printed in progressively larger text, each labeled with a diopter value. The first line you can read clearly corresponds to the strength you need.
If you don’t have a chart handy, the in-store trial works too. Grab a pair of +1.00 readers, hold a book or your phone at normal reading distance (about 14 inches), and see if the text looks sharp. If it’s still blurry, move up one step at a time. Stop at the lowest strength that makes text comfortable and clear. Picking a stronger pair than you need won’t improve clarity and can cause eye strain.
Computer Glasses Use a Different Power
Reading glasses are designed for a distance of about 14 inches, which is where you’d hold a book or phone. A computer screen sits farther away, typically 20 to 26 inches. Because of that extra distance, you need less magnification for screen work. The general rule is about 60% of your reading power. So if you use +2.00 readers for books, a +1.25 pair is a better fit for your monitor.
Using full-strength readers at your computer forces your eyes to work harder to pull the screen into focus at that intermediate distance. Over time this leads to fatigue, blurred vision, and tension headaches, especially during long work sessions.
Signs You’re Wearing the Wrong Strength
Too strong and you’ll notice headaches after 15 to 20 minutes of reading, or you’ll find yourself pushing the book farther away to compensate. Too weak and text stays slightly fuzzy, and you may catch yourself squinting or leaning in closer. Either mismatch can cause general eye fatigue, a pulling sensation behind the eyes, or mild nausea.
Double vision or persistent discomfort with any over-the-counter pair can signal a different issue. OTC readers use the same lens power in both eyes, so if your two eyes need different strengths, or if the distance between your pupils is unusually narrow or wide, store-bought readers won’t line up properly with your line of sight. In those cases, prescription lenses with individually calibrated powers for each eye solve the problem.
When OTC Readers Aren’t Enough
Over-the-counter readers work well for straightforward presbyopia when both eyes need roughly the same correction. They stop being a good option when your eyes differ by more than 0.50 diopters, when you also need distance correction, or when you have astigmatism that blurs text no matter what strength you try. Bifocals or progressive lenses handle those situations by combining distance and near correction in a single pair.
If you find yourself swapping between multiple pairs of readers throughout the day, or if you’ve moved past +3.25 and still can’t read comfortably, a comprehensive eye exam will pinpoint exactly what each eye needs and rule out other conditions like cataracts or glaucoma that can quietly change your near vision.