Eyeglass Frame Size Calculator

How it is calculated

Both inputs are in millimetres: face width (measured straight across the face at temple level) and PD, the distance between pupil centres. The bridge is estimated from the face width and kept between 16 and 20 mm: bridge = clamp(round(face width ÷ 7), 16, 20). The frame width is set equal to the face width, and the two side pieces outside the lenses are taken as about 8 mm each. The rest is shared by two lenses: lens = (face width − bridge − 16) ÷ 2. Values are shown in whole millimetres, so a half-millimetre lens width is displayed rounded up. PD is only checked, not used in the formula: the tool shows no result unless face width is 100–170 mm and PD is 40–80 mm. It gives no temple length, so treat the output as a starting point and compare it with the numbers printed inside a frame that already fits you.

Common mistakes

• Entering PD in centimetres or as two monocular values. The field expects one total distance in millimetres, such as 63, not 6.3 or 31.5; a value outside 40–80 gives no result.
• Expecting PD to change the frame size. It is only range-checked, so two people with the same face width but different PD get the same lens and bridge widths.
• Measuring face width over the cheekbones or around the head instead of straight across at temple level; the tool also rejects values outside 100–170 mm.
• Expecting a frame width different from the face width. By construction they are equal, so the tool does not model how far a frame should overhang or sit inside your face.
• Ordering lenses from these numbers alone. Fit also depends on temple length, nose pad shape and lens height, none of which are calculated here.