I agree, an excellent contribution to an important subject. I wonder, however, whether an exclusive focus on one dimension, foot length, is informative enough. Foot width is also a key factor. The problem is that most fin manufacturers only size their fins in foot lengths.
Do you know that the Deutsches Institut für Normung (DIN), the German Standards Institute, has a National Standard (DIN 7876) dated October 1980 and entitled Tauch-Zubehör: Schwimmflossen: Maße, Anforderungen und Prüfung [official translation: Diving accessories for skin divers; Flippers, dimensions, requirements and testing]? It focuses exclusively on the relationship between foot-width and foot-length when designing the foot pockets of closed-heel ("Form A") and open-heel ("Form B") fins.
Foot length is expressed in millimetres. The length measurement is straightforward for closed heel fins. It's the distance from one extreme end of the foot pocket at the heel to the other extreme at the toe. In the case of open-heel fins with adjustable straps, it's the distance between the extreme toe end of the foot pocket and the extreme position of the heelstrap when it is adjusted to its largest scope possible.
Foot width is also expressed in millimetres. In the case of full-foot fins, the measurement is taken across the inside of the foot pocket at the point where the toes merge with the foot. Foot width in open-heel fins is measured at the widest point of the inside of the foot pocket.
Note that it is the fin itself that is measured under this procedure, which DIN 7876 claims is fully compatible with the Mondopoint system of shoe sizing. The German Standard contains a table stating which foot width (e.g. 75 to 85 mm) should go with which foot length (e.g. 210 mm) for closed-heel fins. The corresponding foot width for open-heel fins with a foot length of 210 mm is 123 mm to 160 mm, the larger size being due to the fact that open-heels are normally worn with socks or boots.
DIN 7876 provides a two-dimensional model of fin sizing. Missing is the foot pocket height dimension. Ignoring this dimension could lead to painful arches in otherwise correctly dimensioned foot pockets.
I'm aware that my intervention may lead to an overcomplication of the data, but I would urge you to take at least the fin foot pocket's length and width dimensions into account. I have an old pair of Italian-made Delfino Marina fins with the following on the sole:
46-48
Size: 11-13
DIN 7876-A
FL. 275
FB. 105
FL is Fußlänge, foot length. FB is Fußbreite, foot width. The numbers are millimetres. DIN 7876-A is the German Standard, the "A" meaning a full-foot fin. Ironically, these fins don't comply with DIN 7876's specifications, because the correct foot width for a foot length of 275 mm is 110 to 115 mm. 105 mm is 5 mm too narrow and, not surprisingly, the fins fit me perfectly length-wise but are too tight for comfort width-wise.
Although there's an almost infinite variety of foot lengths and widths among the general population, individual foot pocket sizes will have a standard length, width and height for a given model. Wouldn't it be helpful to know that closed-heel fin foot pocket R, sized 44-46, is X mm long, Y mm wide and Z mm high? And if that's too much trouble, at least let's get some idea about foot width so we can address the issue of narrow and broad feet!
PS. I have been back to the "submit" page and I note that people are asked to enter their own foot length and width in millimetres, as the Mondopoint system requires, so two dimensions are indeed factored into foot size. I still think that it would be useful to perform the same measurements on the fins themselves, to reduce the otherwise inevitable subjectivity of people's opinion whether the foot pocket fits their feet or not.
