Made in our UK lab · Next Day Delivery
How Do You Know What Strength Reading Glasses to Get?
Published by Direct Sight | Eye Care Guide
Strength. Power. Dioptre. Plus something. The numbers on reading glasses can feel opaque if nobody has ever explained what they actually mean. This guide walks you through exactly how reading glasses strength works, how it relates to your specific eyes and tasks, and the most reliable ways to find the right number.
What the number on the lens actually means
Reading glasses strength is measured in dioptres, the unit optometrists use to measure the focusing power of a lens. A dioptre represents the reciprocal of a focal length in metres. In practice, you don't need the maths, what matters is that a higher dioptre number means a more powerful lens that provides more magnification for near tasks.
Reading glasses always have a plus (+) prescription, such as +1.00, +1.50 or +2.00. The plus sign means the lenses help your eyes focus more easily on close-up objects. The higher the number the stronger the lens power.
Ready-made reading glasses range in strengths from +0.75 to +3.50, increasing in 0.25 steps. Prescription reading glasses can go beyond this range and can also have a different strength in each lens, something off-the-shelf readers cannot provide.
The age-based starting point, and why it is only a starting point
Presbyopia, the age-related stiffening of the eye's lens, progresses on a broadly predictable curve. This allows a rough age-based guide to reading strength that gives most people a reasonable starting point:
| Age range | Approx. starting strength |
|---|---|
| 40-44 | +0.75 to +1.00 dioptre |
| 45-49 | +1.00 to +1.50 dioptre |
| 50 to 54 | +1.50 to +2.00 dioptre |
| 55 to 59 | +2.00 to +2.25 dioptre |
| 60 to 64 | +2.25 to +2.50 dioptre |
| 65+ | +2.50 to +3.00 dioptre |
Use this table as a general guide, not an exact prescription. Presbyopia develops differently for everyone, and your existing distance prescription also affects the reading strength you need. For example, people who are long-sighted often need reading glasses earlier and at a stronger power than those who are mildly short-sighted.
Reading distance matters, more than most people realise
One of the most overlooked variables when choosing reading glasses strength is the distance at which you perform the task. Dioptre strength is not a fixed property of your eyes, it is relative to how far away the object is. The closer the focal distance, the more power is required.
Standard reading glasses are optimised for a focal distance of approximately 30 to 35cm, the typical distance for a book, newspaper, or phone held in the hand. But not all close tasks sit at that distance:
Book or phone screen
Standard reading strength applies here. This is the distance most dioptre guides and age-based tables assume.
Computer monitor
Screens sit noticeably further away than a book. A reading strength calibrated for 30cm will be too strong for a monitor, potentially causing blurred vision or forcing you to lean forward uncomfortably.
Sheet music or kitchen counter
Similarly, any task at arms' length or slightly beyond sits in an intermediate focal zone that standard reading glasses don't serve well.
This is one reason why people who spend most of their reading time at a screen often find that the strength that works perfectly for a paperback feels slightly 'off' on the computer. The distances are genuinely different, and they require genuinely different optical solutions.
Reading the ADD value on your prescription
If you already have a glasses prescription from an optometrist, the information you need for reading glasses will be provided on it. For anyone who needs reading correction, the prescription will include a value labelled 'Add', 'Near Add', or 'NV' (near vision). This is the additional focusing power prescribed specifically for near tasks, applied on top of your distance correction. You can learn more about all the values on your prescription in our guide to understanding your glasses prescription.
The ADD value is always a positive number, typically ranging from +0.75 to +3.00, and it is usually the same for both eyes. To calculate your single vision reading prescription, you add the ADD value to the sphere (SPH) for each eye. So if your distance prescription is -1.50 in each eye and your ADD is +2.00, your reading prescription is +0.50. If your distance prescription is plano (zero) and your ADD is +1.75, your reading prescription is +1.75 in each eye.
For those who also have a distance prescription a simple ADD value on a pharmacy shelf reader will not be to the correct lens strength. This is where prescription reading glasses become genuinely necessary for comfortable, accurate vision.
Signs your current strength isn't right
Whether you're wearing glasses you've picked up from a rack or an older prescription, the following signals suggest the power is wrong:
- Too weak: You're still holding the page further away than feels natural. Text looks clear at a distance but blurry at normal reading distance. You feel strain after short reading sessions.
- Too strong: Text is sharp only when held closer than feels comfortable. You feel immediate dizziness or nausea when putting the glasses on. The edges of your visual field look distorted.
- Either: Headaches developing during or after reading. One eye feels more strained than the other, which can indicate your eyes need different strengths from each other.
If any of these apply, arrange an eye test rather than simply trying a different shelf strength.
Why an eye test is the gold standard
Self-selecting ready readers has fundamental limitations. The most important is this: an age-based guide or a dioptre chart can estimate the magnification your eyes need. It cannot tell you whether your two eyes need different strengths, whether astigmatism is contributing to your blurred near vision, or whether any other refractive condition is influencing the result.
A registered optometrist measures your ADD value during an eye test, taking into account the prescription in each eye. This is the only way to get a reading strength tailored accurately to your vision rather than an estimate.
Once you have your prescription, you can browse Direct Sight’s range of prescription reading glasses, with prices starting from £9.00 and lenses made in our UK laboratory. If you haven’t had an eye test within the last two years, this should be your first step before buying new reading glasses.
Ready to order reading glasses online?
Browse our range of frames and customise with your accurate reading prescription.
Related Categories
Frequently Asked Questions
What dioptre strength do I need for reading glasses?
The right strength depends on your age, your existing distance prescription (if any), and the focal distance of the task you're correcting for. As a rough starting guide, those in their early 40s typically begin around +1.00, progressing to +2.50 or above from the mid-60s. However, these are generalisations, if your eyes have different correction needs, or if you have any degree of astigmatism, the only accurate way to determine the right strength is through a professional eye examination.
Is there a difference between reading glasses strength for a book and for a computer?
Yes, and this matters more than most people expect. Book reading typically happens at about 30 to 35cm; a computer monitor usually sits at 50 to 70cm. A lens optimised for the closer distance will be too strong for the screen, potentially blurring the monitor or causing you to hunch forward.
If you spend significant time at a screen, a weaker reading strength or a dedicated intermediate (computer) lens set to the right focal distance will be considerably more comfortable than repurposing a standard reader.
What does the ADD value on my prescription mean?
The ADD (or Near Add) is the additional focusing power your optometrist has prescribed specifically for close-up tasks. It is always a positive number, typically between +0.75 and +3.00, and represents the extra correction needed on top of your distance prescription to focus clearly at reading distance. To calculate your single vision reading prescription, you add the ADD value to the sphere (SPH) for each eye. See our prescription guide for a full explanation of all the values you'll find on your prescription.
Can I use the same reading glasses for both eyes if my eyes are different?
If your eyes have different prescriptions, using the same strength in both lenses means at least one eye will be either over- or under-corrected. This is a limitation of all off-the-shelf readers, both lenses are always the same power.
Prescription reading glasses are made to your exact prescription and can include different lens strengths for each eye, precisely tailored to your individual vision needs. For anyone with a noticeable difference between their eyes, prescription glasses are the only reliable way to avoid unnecessary eye strain and keep vision balanced.
Should I choose a stronger or weaker strength if I'm between two options?
Always choose the weaker of the two strengths. A lens that is slightly weaker than ideal usually just requires a small amount of extra focusing effort, which most people tolerate well. A lens that is too strong, can cause more noticeable discomfort, including headaches, dizziness, eye strain, and a feeling that the glasses are making vision harder rather than clearer.
When comparing strengths, always test them at your normal reading distance rather than simply choosing the option that looks clearest when held further away.
My reading glasses worked well for a year but now feel too weak. Should I just go one strength higher?
It's tempting, but having a professional eye test the recommended option. Presbyopia does progress naturally, and a modest increase in the reading prescription is often the straightforward explanation. However, a change in near vision can also sometimes reflect changes in distance prescription, the development of early cataract, or other conditions that are worth ruling out. An optometrist can confirm whether a simple prescription update is all that's needed or whether something else warrants attention.
Can I get prescription reading glasses online without visiting an optometrist?
Yes, once you have a current prescription issued by a registered optometrist, you can order prescription reading glasses online from any optical retailer in the UK.
You are entitled to take your prescription wherever you choose to purchase glasses. At Direct Sight, all lenses are made in our UK laboratory to your exact prescription, starting from £9. If you also need correction for different distances, reading and driving, for example, varifocal and bifocal options are also available.
References
NHS, eye Tests: What to Expect and Who Is Entitled
NHS, presbyopia: Overview, Symptoms and Treatment
College of Optometrists, clinical Management Guidelines: Presbyopia
College of Optometrists, prescribing Spectacles (Guidance)
Look After Your Eyes, your Optical Prescription Explained (ADD value)
Royal College of Ophthalmologists, patient Information: Refractive Errors
RNIB, reading Glasses and Visual Aids
MedlinePlus (US National Library of Medicine), presbyopia
All About Vision, how to Read an Eyeglass Prescription (ADD value explained)
General Optical Council (GOC), standards of Practice for Optometrists and Dispensing Opticians