Glasses Frame Size: How to Read the 50-18-140 Numbers
How to read the three numbers on your frame (lens width – bridge – temple) and what each measurement means, plus generic face-shape styling guidance. Factual optical standards for the measurements; the styling tips are taste, not a rule.
How to read your frame size, not a fitting. The three numbers stamped inside a frame (e.g. 50-18-140) are, in order, lens width, bridge width and temple length in millimetres. The face-shape guidance is generic styling — "frames that generally flatter", taste-dependent, not a rule. For pupillary distance (PD), a prescription or an exact fit, see an eye-care professional.
| Measurement | Typical range | What it is |
|---|---|---|
| Lens width (eye size) | 40–60 mm | The horizontal width of one lens at its widest point, in millimetres. The FIRST of the three numbers stamped on a frame (e.g. the 50 in 50-18-140). Also called 'eye size'. Typically 40-60mm; <=50mm reads small, 51-54mm medium, >=55mm large. |
| Bridge width | 14–24 mm | The distance across the bridge between the two lenses — where the frame rests on the nose. The SECOND of the three numbers (the 18 in 50-18-140). Typically 14-24mm; a smaller bridge suits a lower/narrower nose, a larger bridge a wider one. |
| Temple length (arm) | 120–150 mm | The length of each arm from the hinge to the tip behind the ear. The THIRD of the three numbers (the 140 in 50-18-140). Typically 120-150mm; 135-150mm are the most common, and the same temple length fits a wide range of heads because the arm curves behind the ear. |
| Lens height | 24–45 mm | The vertical height of a lens. NOT printed on most frames but important for progressive / bifocal lenses, which need enough height (commonly ~30mm+) to fit the distance, intermediate and near zones. Slim/narrow frames can be too short for progressives. |
| Total frame width (temple-to-temple) | 125–150 mm | The full horizontal width of the front of the frame, hinge to hinge. Roughly = (2 x lens width) + bridge width + the rims. The single best number for matching a new frame to one that already fits you; compare total width before lens-width alone. |
| The three-number frame size (how to read it) | format: lens_width - bridge_width - temple_length (mm) | Modern frames print three numbers inside the temple arm or behind the bridge, e.g. '50-18-140' (sometimes separated by a small square symbol). They are ALWAYS in this order and in millimetres: lens width, bridge width, temple length. Read them to compare a new frame against a pair you know fits. |
Frames that generally flatter, by face shape
| Face shape | Generally flattering frames |
|---|---|
| Oval face | The most versatile face shape — most frame styles work. Frames slightly WIDER than the broadest part of the face keep the natural balance. Generic styling guidance, not a rule. |
| Round face | Soft, curved features with similar width and height. Angular / rectangular / geometric frames add definition and lengthen the face. Avoid round frames (they mirror the face). |
| Square face | Strong jaw and broad forehead of similar width. Round and oval frames soften the angles and add balance. Avoid boxy / sharply rectangular frames (they exaggerate angularity). |
| Heart-shaped face | Wider forehead narrowing to a pointed chin. Frames that are wider at the bottom, plus round and aviator styles, balance the narrower chin. Light / rimless frames also flatter. |
| Diamond face | Narrow forehead and jaw with wide cheekbones. Round, oval and cat-eye frames soften the cheekbones and add width at the brow. Frames with detailing on the top rim flatter. |
| Oblong / rectangular face | Longer than it is wide. Frames with more DEPTH (height) than width, and decorative or contrasting temples, add width and break up the length to balance the face. |
| General fit rule (balance, don't mirror) | The core styling convention: choose a frame shape that CONTRASTS your face shape rather than mirrors it — round frames on a round face or boxy frames on a square face exaggerate features instead of balancing them. Taste-dependent guidance, not a measurement or rule. |
Frequently asked questions
What do the numbers on my glasses mean?
They're lens width, bridge width and temple length in millimetres, always in that order (e.g. 50-18-140). Match them to a pair you know fits.
Can you tell me my prescription or PD?
No. This is a measurement reference only. For your prescription, pupillary distance or an exact fit, see an eye-care professional.