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Total width = left side width + left lens width + bridge width + right lens width + right side width

I've just sent out an email to one of the sites that doesn't provide a "total width" measurement on the frames asking them to start providing it.

Until that happens (and with other sites that don't provide it), here is how you can come up with that number with nothing more than a ruler, your monitor, pencil and paper, and some junior-high math.

Here's how it works:

There is a way to get a pretty decent estimation if you can get a decent photo of the front of the frame (in any size) and have the actual lens width measurement. Using a simple equation solving for 'x'.

In the (fabulous) sketch above, 47 is the actual lens width. 22 is the measured width (in mm) on the printed photo, and 4 is the measured width (also in mm) from the outside edge of the lens to the very edge of the frame. Solving for x you get the following (47 x 4)/22 = 8.545454 (or effectively 8.5) for the external width.

Multiply your known lens width by 2, add the known bridge width, and add your solved-for temple width multiplied by 2 and you have a total width.

In this case, (47 * 2) + (8.5 * 2) + 19 = 130mm.

In the meantime, I'll continue to PLEAD with them to save us from this silliness.

Hope this helps.

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At May 29, 2009 at 7:09 PM Arlynda said...

That's great, but I'm laaaazy. I just held my glasses up to the nearest ruler (non-metric), got a measurement from earpiece to earpiece of 5 1/8", googled me up an inches-to-millimeters conversion calculator, and got 127 mm.

Is there some reason why this method would be less accurate (other than, say, being too blind to read the ruler accurately)?

At May 29, 2009 at 7:14 PM Ira said...


Sure your method works when you're holding the frame...

But what about when you're trying to choose a frame online?


At May 30, 2009 at 12:56 PM mrnumi said...

Your formula is accurate and the math works out, but for some reason you cross-multiplied 50 with 4 instead of 47. You got the answer (approx 8.5) that you should have gotten had you used the 'actual' measurement of 47. Using 50 will have x equaling approx. 9.09.

Yeah, 1 mm isn't going to make much difference. But you should probably correct it so that people who aren't so great with math (myself included) can follow your example better.

At May 30, 2009 at 2:29 PM Karen said...

Hi Ira,
Thank you very much your blog and links and to all yours readers for their comments too. I just received my glasses order from Coastal Contacts (one week from ordering to my door on the opposite coast), and for $25 ($19.99 frame plus shipping.) I have a great new pair of glasses. I do have a "whoa!" moment of adjustment when I put them on though. (Maybe I need to double-check the PD measurement or something?) I'm a new fan of online glasses; I'm not sure that I could afford new glasses otherwise. Thank you, thank you!

At June 6, 2009 at 1:36 PM Anonymous said...

Thank you, Ira! Total front width is one of the MOST important measurements for deciding on any given frame-(being the main measurement that will show what frame will, or will not, fit a persons face)-and PLENTY of online retailers DON'T provide it. You either have to email them, or be "out in the streets" when some just wont email you back. It's especially hard for someone like me who needs a "larger" frame size. I'm comfortable at 140mm. So I need at least a 138mm or more. This makes the total front width measurement even more important, as most sites usually carry most of their stock on the 120mm-130+mm range. It must be SPECIFIC and spelled out! Keep fighting the good fight!

At June 22, 2009 at 5:05 PM Muriel said...

Thanks for this (and the all blog). However i ordered some glasses from google4u and i just can't wear them. I just measured : the frame is 130 mm BUT the width at the ear level (where you put them on your ears) is at most 124. I don't see any notice of this measurement anywhere, but geez, after 10 min, i had a terrible headache. Just FYI...


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