Don't even try to measure your insole, you´ll never get it right. Just look at the measurements on any of your sneakers in CM or CHN. Then take that information and find the corresponding US size in the size guide. For example, the insole length of 25 CM corresponds to US 7 in Vans. You may get a different US size with a different brand due to slightly different measuring.
Diadora is an Italian brand producing sports equipment since 1948 for football, tennis, athletics or even rugby. Nowadays Diadora got into the world of sneakers with their comfy sneakers in exciting color combinations.