Don't just go off a chart with cm lengths - print out the tool where you draw the point of each big toe, and go with whichever size is bigger.Looking at that chart I misspoke. My foot measures right around 26cm so more like an 8. Does that mean I need a size 8, or are they saying their size 8 shoe measures 26cm total?
As many have mentioned here - and Vivo suggest too - if you're between sizes, size up.
It's pretty simple - just be sure to mark each foot, accurately. Follow their instructions closely and it should work.