What Do The Numbers On Glasses Mean?

Most glasses have a series of numbers which is generally located along the inside of the right side arm. But what do these numbers mean? 

They relate to the measurements and overall size of the glasses and are usually in the format 49-19-140

In this example the first number, 49 relates to the horizontal width of the lens in millimetres. 

The second number, 19, relates to the bridge width and the third number is the length of the side arm from the temple to the tip of the arm. It is usually measured before the bend is put on the arm. 

Understanding what the numbers on the glasses mean is particularly important for those who are buying glasses online as these measurements can be used to determine if a pair of glasses will be too narrow, too wide or just right. Most websites will have a glasses size chart that can be very helpful when it comes to choosing the correct size 

The total width horizontally across the full frame can be calculated by multiplying the first number by 2 and adding the second number plus 6mm for the average end widths. The the above example that looks like this, (49 x 2) + 19 + 6 = 123mm 

To measure the width of your face you should stand in front of a mirror, look straight ahead and measure the distance between your two temples. 

The total face width distance should be within 4-5 mm of the total frame width and if this is the case then the glasses will be a good fit. 

Since the numbers on the glasses do not give a total frame width measurement if you know your total face width a quick way to see a pair of glasses would be a good fit is to take your total face width in millimetres, minus the bridge width, minus 6mm (average end widths) and divide the number you get by 2. If this is close to the first figure on the side of the glasses (lens width) then it will be a good fit. 

So for example if your total face width is 125mm, then for the glasses above we have 125-19-6 = 100 100/2 = 50mm 

As the lens width in the above example is 49mm then we can see those glasses would be a good fit. 

Your glasses prescription

Your glasses prescription will be broadly broken down into two types. 

Near-sighted prescriptions will have a minus number, such as -1.00 DS (diopters) 

and farsighted prescriptions will have a plus number, such as +2.50 DS on your eye prescription chart. 

If you are near sighted that means you can see things clearly up close but have difficulty seeing in the distance and the opposite is true for far sightedness. 

If your eyes are perfectly spherical you will only have one number for your prescription. 

If your eye is more of an oval shape you will have one number which is again a plus or a minus and in addition to this you will require extra power in your lenses along a certain axis which will look something like this. 

-2.00/-1.25 x 140

In this example we can see that the patient is near sighted (from the minus sign) and that in their lenses there will be an extra -1.25 diopters of power along the 140 degree axis. The additional power required for a slightly oval shaped eye is called astigmatism. 

In order to focus light onto one point at the back of your eye you would need extra power along a certain axis. The cyl value is that extra power measured in diopters and the axis is measured in degrees between o and 180 and describes the orientation of the extra power. 

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