You may have noticed three numbers printed inside the temple of a pair of glasses, such as 49–20–145. They're useful, but they don't tell you everything about how a frame will look or feel.
What the three numbers mean
The first number is normally the lens width, in millimetres. The second is the bridge width, the distance between the lenses as defined by the frame's bridge sizing. The third is the temple length, which describes the arm length. These dimensions help you compare one frame with another, particularly if you already own a pair that fits well.
Why two frames with the same numbers can feel different
A 49 mm lens width doesn't tell you the entire shape of the lens opening. A narrow rectangle and a soft square can share that measurement while having different lens heights, contours and overall front widths.
Bridge construction, nose-pad design, the curve of the front and the position of the temples can also affect how a frame sits. That's why the numbers are a reference point, not a promise of a perfect fit.
Why prescription strength makes frame choice more important
The relationship between frame dimensions, lens shape, lens material and where your pupils sit can influence how a finished pair looks and feels. With a stronger prescription, frame selection deserves particular attention. A smaller frame can sometimes help with lens thickness, but that is not an automatic rule: prescription details and fitting measurements matter.
We encourage comparing verified frame measurements alongside the shape you enjoy wearing. For specialist lenses, ask for an appropriate optical check rather than choosing on photographs alone.
Start with the pair you already like
If your current glasses are comfortable, look inside the temple for the measurements. Note what you enjoy about the shape, how the bridge sits and whether you find the temples too long or short. It gives you a more reliable place to begin than rigid face-shape rules.
For a closer look, read our frame size and fit guide, explore Find your frame, or see why we approach stronger prescriptions with extra care.
Good design is worth enjoying. Good fit is worth understanding.