How to Convert Your Eyeglass Prescription to Reading Glasses


If you need to convert your eyeglass prescription to reading glasses, you may decide to skip this manual process and speak with your eye care professional. There is nothing inherently wrong with this. But having said that, it is always helpful to know how you can accurately complete this conversion process.

If you are an individual who experiences sustained eye issues, you may have developed some habits and workarounds to make life easier. You may place your eyeglasses in a certain place at home so that you know you won’t lose them when you go to sleep. You may even have a separate pair of eyeglasses that you can wear when you are playing tennis, golf or another one of your favorite sports. Whatever the case may be, you have likely developed a routine that keeps you seeing as clearly as possible.

Nevertheless, there may be situations where you need to abandon some of these manual workarounds in order to see more clearly. As just one example, you may be happy with your eyeglass prescription, but you are having more trouble reading. This can be true whether you are trying to read the day’s newspaper at your kitchen table or an important work document on your computer.

Yes, you can squint and try to power through your vision issues. But having said this, there may come a time when you need to convert your eyeglass prescription to reading glasses. While this isn’t necessarily a difficult task, it is not something that you can simply breeze through. It can be easy to trip up. Therefore, it is critical to recognize and understand the common steps in this process.

We are here to help. At Rx-Safety, we sell all different types of glasses—including prescription glasses. We have seen the conversion process many times, so we want to do our part to demystify this process. 

Below you will find our guide to converting your eyeglass prescriptions to reading glasses. By following the steps and advice that we have presented below, you will be well on your way to completing this important task.


The Conversion Process

To convert to reading glasses, you only need two things. You will need your current eyeglass prescription and a calculator. From there, you will do some simple math to ensure that your conversion is accurate.

Let’s start with your current eyeglass prescription. Every eyeglass prescription contains several abbreviations and numbers. For instance, “OD” stands for oculus dexter (“right eye” in Latin) and “OS” stands for oculus sinister (“left eye”). To successfully convert your eyeglass prescription to reading glasses, you will need several other metrics. You will need a distance prescription, sphere power, and an add. The distance prescription is self-explanatory. Sphere power is the main strength of your eyeglass prescription, and it is written in increments of 0.25. The add stands for the additional correction that is used for reading glasses.

Essentially, the formula for converting an eyeglass prescription to reading glasses is adding your sphere power to your add power. To illustrate this process, it is helpful to provide some examples.

For instance, let’s say that you have an eyeglass prescription that has a sphere power of -1.25, a cylinder of -1.00, an axis of 83, and an add of 1.50. Once again, the formula states that we should add our sphere power (-1.25) to our add power (1.50), resulting in plus 0.25. From here, if this were to become a single vision reader, the end result would be plus 0.25, minus 1.00, at 83 degrees.

As another example, if we had a sphere power of 2.00, a cylinder of -1.50, an axis of 130 degrees, and an add of 1.50. We would follow the same steps as above. Simply put, we would add the sphere power of 2.00 to the add of 1.50, resulting in plus 3.50. The final prescription reading for these reading glasses would be plus 3.50, minus 1.50, at 130. By this point, you can see that both the cylinder and axis are never going to change. The only thing that will change will be the sphere power because we are adding the added power to it. Simple enough, right?

This conversion formula can lead to some interesting scenarios. For instance, if you have a sphere power of -1.50 and an add of 1.50, you will end up with 0.00. You would be wearing a single vision reader of 0.00 and this will be included with the same cylinder and axis.

The situation becomes somewhat more complicated if your sphere power is not the same for both eyes. As just one example, let’s say that your right eye has a sphere power of -3.50 and your left eye has a sphere power of -2.75. The remaining parts of your prescription are the same for both eyes. For instance, let’s assume that your cylinder is -0.75, your axis is 140 degrees, and your add is 1.50. From there, you would follow the same formula as described above. Specifically, you would take your right eye sphere power of -3.50 and add it to your add (1.50), resulting in -2.00. For your left eye, you would take -2.75 and add it to 1.50, equalling -1.25. This would result in a right eye of -2.00, -0.75 at 140, and a left eye of  -1.25, -0.75 at 140. It is as simple as that.


As you can see, the math itself isn’t that tricky. The one thing that could trip you up, however, is the addition of both positive and negative numbers. It is easy to mix your signs, which could result in reading glasses that are not properly converted for your eyesight. Because of this, it doesn’t hurt to have a calculator when you are doing this conversion. Take your time and don’t hesitate to check your math twice. If you put on your reading glasses and think that something is off, go back and see if you correctly made your conversion. While you will eventually get it right, you can avoid some frustration and wasted time by going slow and checking your math.

how to fill out your eye prescription

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How to convert your prescription glasses into reading glasses


Sphere power

+ Add power


Original prescription







+ ADD:


Confidently Converting Your Eyeglass Prescription to Reading Glasses

By this point, we hope you have realized that it isn’t an extremely complicated process. Yes, it does require you to do some simple algebra. If you feel like you’re weak at math, you may be intimidated by this fact. Luckily, however, the algebra is extremely basic. Slowing down, being deliberate, and checking your work is an effective playbook here.

Therefore, we encourage you to try it out for yourself today. If it would make you feel more comfortable, feel free to do some hypothetical conversions first. Completing practice conversions before real-life conversions will make you more comfortable with the math and will give you the confidence to move forward. Once you are more confident, however, feel free to try the conversion on yourself. If you accurately complete the conversion, that’s great! If not, you will quickly notice, and you can course-correct as necessary.

We wish you the best of luck!

  1. Joesph says:

    Does it matter if the cylinder is in the positive. I noticed all the examples, the cyl was always negative.
    So what readers would be needed? Thanks
    OD -1.75 +0.50 080 +1.00
    OS -4.00 sph +1.00

  2. fb33c says:

    I’m admittedly a bit confused. I just got my Lens RX. They originally gave me 2 separate prescriptions for Distance & Reading. I asked them for a single Progressive RX and for the life of me the ADD just looks off. Can you confirm the ADD is correct?

    Distance: OD: Sphere -0.50/ OS: Sphere -0.75, Cylinder D.S.
    Reading: OD: Sphere +1.00, Cylinder D.S. / OS: Sphere +1.00, Cylinder D.S.
    Progressive: OD: Sphere -0.50, Cylinder D.S., ADD +2.25 / OS: Sphere -0.75, Cylinder D.S., ADD +2.25

    Cylinder D.S. across the board.

    • b.kotian says:

      Hi fb33c,

      Thank you for reaching out. For the most accurate verification of your prescription, I recommend consulting with your eye doctor to confirm the ADD and ensure all details are correct.

  3. Robin Jackson says:

    My prescription is:
    Right eye

    Sphere 1.75
    Cylinder -0.5
    Axis 84.0
    Add 2.5

    Left eye

    Sphere 1.5
    Cylinder -0.5
    Axis 118
    Add 2.5

    What would I need for cheaters?

    • b.kotian says:

      Hi Robin Jackson,
      Your reading glass prescription is
      Right eye: Sphere +4.25, cylinder -0.5, Axis 84.0
      Left eye: Sphere +4.00, Cylinder -0.5, Cylinder -0.5

  4. John says:

    My bifocal prescription is:
    Right: SPH = -1.50, CYL = -0.75, Axis = 90, ADD = +0.75
    Left: SPH = plano, CYL = -2.75, Axis = 80, ADD = +0.75

    Could you tell me what my reading prescription would be?

    • b.kotian says:

      Hi John,
      Your reading glass prescription is
      Right: SPH = -0.75 , CYL = -0.75, Axis = 90
      Left: SPH = +0.75 , CYL = -2.75, Axis = 80

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