Different manufacturers write out measurements slightly differently, which can make reading the measurements seem daunting, but just remember to look for the series of 3 numbers. For example, the same measurement could be written “Brand Model 45/20 135,” “45-20-135,” or “45 20-135. ” Any words or numbers grouped together with capital letters, such as “ESJ-213” or “O17,” represent the frame style or color. Don’t worry about these, since they aren’t relevant to the size measurements.

For example, if your measurements are “45 20-135,” your eye size would be 45 millimetres (1. 8 in). For bifocals and progressive lenses, manufacturers will often break down the lens width and height into separate measurements.

For example, if your measurements read “45 20-135,” your bridge size would be 20 millimetres (0. 79 in).

For example, if your measurements are “45 20-135,” your temple length would be 135 millimetres (5. 3 in). Some of the most common arm measurements include 135 millimetres (5. 3 in), 140 millimetres (5. 5 in), 145 millimetres (5. 7 in), and 150 millimetres (5. 9 in).

Measure horizontally across one lens at its widest point to find your lens width. Place the ruler over the top of the glasses and measure from the inner edge of one lens to the other to find your bridge size. To find your arm length, measure from one of the arm hinges to the point where the arm begins to curve to fit over the ear. If you have trouble finding your measurements, you can also have an optician take them for you.

For example, if your glasses keep slipping down your nose, your bridge width may be too wide. Look for a pair with a shorter bridge measurement. If your glasses pinch your nose or the sides of your head, they are likely too small. Choose a new pair with higher measurements for a better fit.

This is especially important when purchasing high-fashion frames. Their measurements often differ from standard eyeglasses styles, so it’s important to try them on before you make your purchase.

Choose glasses that are slightly wider than your face for the most flattering effect. If there’s more than a finger’s width of space between the temple of the glasses and the side of your face, the glasses are probably too wide. Instead, look for a pair with a smaller eye size.