Dime = informal Digame = Formal

dime es informal y digame es formal, ejemplo, cuando estas hablando con un amigo y el te llama tu solo le dices dime carlos algo asi, pero cuanod es con tu jefe uno dice digames mr, ferradas. ya ves??? espero haberte ayudado con tu duda

"Dime" and "digame" are composed of the verb "decir" in the imperative form and the pronoun "me". "Di" corresponds to the imperative of the second person (tú: you). And "Diga" to the third person (he/she: él/ella). Why then do you say "diga" when you are referring to "you"?? Just because, in spanish, the formal way to address to a person is calling him/her "Usted" (which is also translated into english as "you", but imagine that it was as if you said "Sir", or "Madam", more or less), instead of "tú". Well, Usted, "surprisingly", is conjugated as if it were the third person and not the second one. For example: "Usted es Juan", instead of "*Usted eres Juan". Well, in your sentence, Usted is omitted, but the mark of the third person in the verb means that you are addressing to someone in a formal way. So, in all cases, you can know if it's formal or not just paying attention to that feature. If the subject is "you" but the verb conjugation is in the third person form, then, it's formal, ok? Ha comprendido (Usted)? Has comprendido (tú)? :)

tu dime cuanto vale usted digame cuanto vale