Different countries use different shoes sizing standards. Sizing can also vary depending on the manufacturer. Sur follow Italian shoe sizing standard and the table below will help you convert it into your size.
Overall Sur shoes run small, so if you are between sizes you will most likely need to go a half a size up as opposed to down, i.e. if your street shoe size is 7.5 you will most probably be a size 38 in Sur.
Overall, please remember that all dance shoes stretch out and if you purchase a size larger than what you need it can become a problem in the future after a few wears. A dance shoe should fit you like a glove and if you are able to stick a finger in between your heel and your shoe's heel cage, then you are definitely wearing a wrong size of tango shoes.