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Switching between progressive lenses and a dedicated pair of readers can make life easier—especially if you love cozying up with a book or working at your laptop without constantly tilting your head. But if you already wear progressives, how do you figure out the correct strength for reading glasses? Let’s break it down simply.

Step 1: Understand the Prescription Terms

Every eyeglass prescription lists values for each eye:

• OD = Right eye
  
  
• OS = Left eye
  
  
• Sphere (SPH) = Corrects nearsightedness or farsightedness
  
  
• Add = The magnifying boost for close-up tasks (used in bifocals and progressives)
  
  

When you want to calculate your reading-only power, you’ll be combining the sphere and the add for each eye.

Step 2: Do the Simple Math

For each eye, just add the sphere number to the add number.

Example:

• OD Sphere: +1.25
  
  
• OD Add: +1.50
  
  
• Reading Power (OD): +2.75
  
  

Do the same for the left eye (OS).

✅ Correct Method: Sphere + Add = Reading Power
❌ Common Mistake: Adding sphere to sphere or add to add

Step 3: Watch Out for Negative Numbers

Sometimes, your sphere number will be negative. Don’t panic—that just means you’re nearsighted. The same math still applies.

Example with a negative sphere:

• OS Sphere: –0.75
  
  
• OS Add: +1.50
  
  
• Reading Power (OS): +0.75
  
  

So, in this case, both eyes would need +0.75 reading glasses.

Myths vs Facts About Reading Power

Myth: “You just need to match the Add number for readers.”
Fact: You always need to add your Sphere + Add. Skipping the sphere gives you the wrong strength.

Myth: “Negative numbers can’t be used for readers.”
Fact: Negative spheres simply adjust the math. Your final reading power can still be positive.

Why This Matters

Using the right calculation ensures your readers match your actual vision needs. Get it wrong, and you risk eyestrain, headaches, or blurry text. Get it right, and you’ll enjoy sharp, comfortable reading—whether it’s a beach novel or tonight’s recipe.

At DebbySpecs, we know readers are more than just a vision tool—they’re a style accessory. That’s why we make sure you understand your prescription before you pick frames you’ll love wearing.

TL;DR

• Take your prescription.
  
  
• Add Sphere + Add for each eye.
  
  
• That’s your reading-only power.
  
  
• Watch for negatives—they still work with the same math.
  
  
• Avoid mixing up Sphere-to-Sphere or Add-to-Add.
  
  

FAQs

Q: What if my Sphere and Add numbers are different in each eye?
A: That’s normal. Just do the math separately for each eye.

Q: Do I need custom prescription readers, or can I buy ready-made ones?
A: If both eyes end up with the same reading power, you can use ready-made readers. If not, prescription readers may be more comfortable.

Q: My Add is +2.00. Does that mean I need +2.00 readers?
A: Not necessarily—you still need to add your Sphere number to that +2.00.

Q: What if the math seems confusing?
A: Don’t worry! An optician (like our friends at My Eyeglass Club) or our DebbySpecs team can double-check for you.

✨ At the end of the day, your reading glasses should sharpen your vision and flatter your look. Once you know your power, you can focus on the fun part: finding the stylish frames that make you feel amazing.