Reading Glasses Calculator
Use this reading glasses calculator to estimate the over-the-counter reader strength you may need, based on your age and reading distance.
Updated October 22, 2026
Medical Disclaimer: This calculator gives a general estimate for education only and cannot diagnose a condition. Share your result with your doctor or the clinician who ordered your test, and do not start, stop or change any medicine based on it. Read our full Medical Disclaimer.
How Reading Glasses Strength Is Calculated
Reading glasses strength is the plus power of the lenses, measured in diopters (D) and printed on the frame, such as +1.50. Readers replace the close-up focusing power your eyes lose with age. This calculator estimates how much is missing at your reading distance.
What Reader Strength Measures
It measures how much extra focusing help a lens gives, not eye health. The need for readers comes from presbyopia, a normal change in which the lens inside the eye gets stiffer and can no longer change shape easily to focus up close¹. It usually shows up in your 40s, gets worse over time, and usually stops getting worse after about 65². Common signs are holding reading material farther away, eye strain and headaches².
The Formula
Both methods use the same idea: the power you need equals the focusing your reading distance demands, minus the focusing your eyes can comfortably supply.
Focusing demand (D) = 100 / reading distance in cm
By age: Reader strength = Age table value + (Focusing demand - 2.50)
By reading distance: Focusing range = 18.5 - (0.30 x age)
Reader strength = Focusing demand - (Focusing range / 2)
The age table comes from a clinical study and is set for a 40 cm reading distance, where the demand is 2.50 D³. The focusing range (amplitude of accommodation) formula is Hofstetter's average for age⁴. Dividing it by 2 follows the clinical rule that comfortable near work should not use more than one-half to two-thirds of your full focusing range³.
How This Calculator Computes Your Result
Enter your age (35 to 100), whether you wear glasses or contacts to see far away, and your reading distance: book or phone (40 cm, 16 in), computer (60 cm, 24 in), or a custom 25 to 100 cm (10 to 39 in, converted at 2.54 cm per inch). "By age" is the default method. The result is rounded to the nearest 0.25 D, the step clinics use for near powers³. The tool also shows the other method's number and your strength at book and computer distance. Under 40, the age method shows that most people do not need readers yet.
What Your Result Means
Your result | What it means |
+0.25 or less | You may not need readers at this distance yet |
+0.50 to +0.75 | A small need, below where most store readers start (+1.00) |
+1.00 to +1.75 | Typical at book distance from about 43 to 52 |
+2.00 to +2.50 | Typical at book distance from about 53 on |
+2.75 to +4.00 | Above the age table's top value, usually from a very close reading distance |
Most store readers range from +1.00 to +4.00⁶. Choose the lowest strength that is clear and comfortable at your usual reading distance⁶. Trying your result and the strengths 0.25 above and below is a simple way to find it.
This is the age table the calculator uses (40 cm reading distance)³:
Age | Typical reading add |
40 to 42 | +0.75 |
43 to 45 | +1.00 |
46 to 47 | +1.25 |
48 to 50 | +1.50 |
51 to 52 | +1.75 |
53 to 55 | +2.00 |
56 to 57 | +2.25 |
58 to 60 | +2.50 |
The table ends at 60. The calculator holds +2.50 for older ages, since presbyopia usually stops progressing after about 65².
Why the Two Methods Can Give Different Numbers
At book distance, the focusing range method usually comes out 0.50 to 1.00 D lower than the age table between ages 45 and 59. A study of 69 people aged 40 to 60 compared seven ways of choosing a reading add³. The age table landed closest to the final prescription, with almost no average error, while a focusing range method based on each person's measured focusing range came out higher on average and varied the most³. That is why "By age" is the default. Even the age method could miss by more than 0.5 D, so both numbers are a starting point³.
Why Computer Distance Needs Less Power
The closer the text, the harder your eyes must focus. A book at 40 cm demands 2.50 D. A screen at 60 cm demands only about 1.67 D, so the reader you need there is about 0.75 to 1.00 weaker. The American Optometric Association suggests placing a computer screen about 20 to 28 inches (51 to 71 cm) from your eyes⁵. This is why book-strength readers can make a screen look blurry. Glasses made for general use may not suit computer work either⁵.
If You Already Wear Glasses for Distance
Store readers suit people who see clearly far away without glasses. Both lenses have the same power, and they do not correct astigmatism or a difference between your eyes⁶. If you already wear glasses for nearsightedness, farsightedness or astigmatism, you may need bifocals, trifocals or progressive lenses, which put distance and near power in one lens¹. The calculator shows this instead of a number. With distance contacts, it assumes your contacts give you clear distance vision. To see how a glasses prescription converts to contact lens power, see our Contact Lens Conversion Calculator.
Signs That Need an Eye Exam Now
Readers fix slow, gradual blur up close. Some symptoms are not presbyopia. Sudden blurry vision with severe eye pain, a red eye, headache, nausea or halos around lights can be an angle-closure glaucoma attack, which is a true eye emergency⁷. A lot of new floaters, flashes of light, or a dark shadow or curtain over part of your vision can mean a detached retina, which is also an emergency⁸. The American Academy of Ophthalmology also advises a complete eye exam around age 40⁷.
Reader Strength by Age and Reading Distance
The calculator's default age method at book distance and at computer distance. Pick your age to read across.
- +0.25 or less may not need readers yet
- +0.50 to +0.75 small need
- +1.00 to +1.75
- +2.00 to +2.50
| Age | Reader strength (D) | |
|---|---|---|
| Book or phone, 40 cm (16 in) | Computer, 60 cm (24 in) | |
| 40 to 42 | +0.75 | Not needed |
| 43 to 45 | +1.00 | Not needed |
| 46 to 47 | +1.25 | +0.50 |
| 48 to 50 | +1.50 | +0.75 |
| 51 to 52 | +1.75 | +1.00 |
| 53 to 55 | +2.00 | +1.25 |
| 56 to 57 | +2.25 | +1.50 |
| 58 to 60 | +2.50 | +1.75 |
| 61 and over | +2.50 | +1.75 |
Use the arrow keys to move between cells.
A Note on Accuracy
This is an educational estimate, not a prescription. Both methods use population averages, and your real need depends on your eyes, any uncorrected nearsightedness or farsightedness, lighting and how far you hold things. The age table comes from a small clinical group at 40 cm, and the adjustment for other distances is an estimate. Readers need no prescription, but the right power is best set by an eye exam¹.
Frequently Asked Questions
What strength reading glasses do I need for my age?
At a 40 cm reading distance, typical adds run from about +0.75 at ages 40 to 42, to +1.50 at 48 to 50, to +2.50 by 58 to 60³. Computer distance needs a weaker strength.
How do I know what strength reading glasses to buy?
Start with the estimate from this calculator, then try that strength and the ones 0.25 above and below. Pick the lowest strength that lets you read clearly and comfortably at your usual distance⁶.
Is a reading glasses calculator accurate?
It gives a reasonable starting point, but even the best age-based method in clinical testing could be off by more than 0.5 D³. An eye exam gives the exact power and checks your eye health¹.
Can I use reading glasses if I already wear glasses?
Not as a substitute for them. Readers have no distance correction, so people who already wear glasses usually need bifocals, trifocals or progressive lenses instead¹.
Sources
What Is Presbyopia?, American Academy of Ophthalmology
Presbyopia, National Eye Institute
Comparing Methods of Determining Addition in Presbyopes, Antona et al., 2008
Diurnal Variations of Amplitude of Accommodation in Different Age Groups, Park et al., 2019
Computer Vision Syndrome, American Optometric Association
Are Cheater Glasses Right for You?, Cleveland Clinic, 2026
What Is Glaucoma?, American Academy of Ophthalmology
Retinal Detachment, National Eye Institute