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.
HUF was founded in 1992 by Keith Hufnagel, who grew up in the streets of New York where he was skateboarding. He became a professional, enabling him to travel around the world. Later he opened a small boutique in San Francisco, it was the first store of its kind, and Hufnagel gradually got all the skate brands under one roof. Today he sells his own apparel, which is also available in the Footshop.