The measurements eyewear retailers publish

Total front width — ear to ear across the face — is the one measurement that answers “will this fit me” without arithmetic. It is also the one retailers leave out. Of the 37 retailers we hold offers from, 6 publish a real front width and 17 publish none at all.

Frame by frame, 12.1% of the catalogue carries a width the retailer stated (4,420 frames). Another 65.7% can only be reconstructed from the parts: twice the lens width, plus the bridge, plus a fixed allowance for the end pieces. For the remaining 22.2%, 8,114 frames, there is nothing to reconstruct from either.

The reconstruction is not a measurement and we do not present it as one. 84.4% of the frames that state a width can also be reconstructed, which is what lets us check the formula against reality rather than trust it.

Lens width is the measurement retailers do publish: 84% of frames state one, 30,689 of them. Stated widths run from 38mm to 79mm, and almost none of that range is where the market is.

91% of every stated width falls between 48mm and 58mm. Three widths — 53mm, 54mm and 52mm — account for 42.4% between them, and 53mm alone for 15.3%.

The tails are thin in both directions and thinner at the narrow end: 2.5% of stated widths are 46mm or under, against 4.8% at 59mm or over. A face that needs a narrow frame has fewer than half as many to choose from as a face that needs a wide one.

Lens height is the measurement varifocal and bifocal wearers are told to check, because a lens that is too shallow cannot fit the reading zone. It turns out to be well published — 83.9% of frames state one, 30,638 of them — and the worry is largely misplaced.

The median stated depth is 42mm. Only 1.5% of frames are under 32mm, the shallowest depth a standard varifocal is commonly sold for, and 0.2% are under 28mm. In frames, that is 454 out of 30,638.

Rim type barely moves the median: 42mm full-rim, 43mm rimless and 40mm semi-rimless. Semi-rimless is the one to watch, with 6.4% under 32mm against 1.2% of full-rim.

Most frames are sold by one retailer and cannot be price-compared at all. Only 1.7% of the catalogue, 618 frames, is carried by more than one shop, and 607 of those carry two live prices to compare. No frame we hold is sold by more than 3 retailers.

Where a comparison is possible, it is worth making. The median gap between the cheapest and dearest price for the identical frame is £10.22, or 10.6% of the cheaper price. At the ninetieth percentile the gap is 98.6%: the dearer shop asks close to double.

That the overlap is small is itself the finding. Comparison shopping for glasses is not mostly a matter of finding the same frame cheaper. It is a matter of finding a frame in the right size at all, which is what the measurement gap in finding one makes hard.

Retailers publish three states, not two. 43.8% of offers are held in stock, 46.2% are ordered in from the brand on request, and 9.2% say neither.

The median in-stock frame costs £69.99. The median order-in frame costs £114.11, which is £44.12 more: a 63% premium.

This is the finding on this page most likely to be measuring something other than what it appears to. Order-in ranges skew towards designer brands, and one large retailer accounts for much of the order-in population, so part of the gap is a difference in what is being sold rather than a charge for waiting. Read it as a description of two populations, not as a causal claim about fulfilment.