The size conversion chart is interesting but apparently flawed.
I'm aware of three National Standards for swim fins and all of them, among other things, cover sizing:
Russian Standard GOST 22469-77 "Lasty rezinoviye dlya plavaniya (Swimming rubber flippers)"
German Standard 7876: "Schwimmflossen: Maße, Anforderungen und Prüfung (Flippers: dimensions, requirements and testing)"
Malaysian Standard MS 974:2002 "Specification for rubber swimming fins"
All these Standards use the Mondopoint system of sizing, which comes down to foot length in millimetres.
Now the (possible) flaws with your conversion chart...
Mexico's (only?) domestic diving equipment manufacturer sizes its fins in foot length centimetres:
VENTA EQUIPO DE NATACION Y BUCEO. Tel. 56732722,56732597, 56737492 - Aletas
I know that the USA has different sizing systems for men and women, but I wasn't aware that the UK, where I live, had different scales for the two genders. In any case, European size 46 is closer to UK size 11 than 12.
I own pairs of Russian- and Ukrainian-made fins, all of which comply with the Russian Standard GOST 22469-77. All are marked "285-295" only, which accomodates my UK foot size 11 (European 46) and corresponds to the Mondopoint system of foot length in millimetres.
Finally, I have to agree with Floridamike: "Nothing will beat trying them on". This is especially true of Malaysian fins, whose sizes tend to "run small".