This is information on the industry-wide standards for sizing all eyeglass (and sunglass)frames. Frames generally are categorized by the eyesize (size of the lens opening), the bridge size (the space between the two lens at the nose) and the temple (earpiece) length. Here will be given an easy method of making these measurements and using them for frame comparisons. Note that eye size and bridge size are given only in millimeters and temples are given in both millimeters and inches, depending on the method used by individual manufacturers.
things you’ll need:
A small millimeter ruler
a cloth measuring tape
1 To obtain the lens size, measure in millimeters one lens from left to right along the 180 (middle) line FROM THE OUTERMOST EDGE OF ONE SIDE TO THE OUTERMOST EDGE OF THE OTHER SIDE. A perfectly round or square lens is easy to measure, but other shapes are more difficult, like a teardrop (pilot) shape. With this shape, your measurement will be completely different along the absolute 180 (the middle) than if you go further out on the point to include the point. Including the point will give you the correct method. Optical labs use this method which will illustrate this: the lens size is obtained by drawing an imaginary square or rectangle around the outermost points of the lens and then measuring across the middle. This will work with any lens shape.
2 Generally, to obtain the bridge size, measure the SHORTEST space between the lens in millimeters. Some manufacturers apply this rule loosely and variances are possible. Also another optical measurement, DBL (distance between lens)is applied. In short, a 20 mm bridge from one manufacturer may not exactly fit like another 20 mm bridge from another.
3 To measure a temple length, measure from the point at which the temple joins the frame front to the end of the temple. A flexible tape (like a cloth sewing tape) can be helpful. This measurement may be stated in millimeters or inches: example a 140mm temple is generally also a 5 and 1/2 inch temple. A 145mm is generally a 5 and 3/4 temple, and so on. Cable temples are always measures in the same way and, if they are very flexible, you can stretch out the springy end and measure with the temple fully extended.
Tips & Warnings
One of the most applicable measurements you can make when measuring and comparing frames, perhaps for purchase, is to get your optician (or do it yourself) to measure the total top measurement. Since we all have fitting needs relative to our face width and preferences as to size. measuring across the very top of the frame, from outermost endpiece to opposite other endpiece (ignoring very horizontally protruding decorations or construction attached to the front, will generally give you a good comparison.
When you are making measurements on a frame which already has lens, be careful not to touch and perhaps scratch the lens.