I'd agree with Steve. Even I can't find a difference between them, from any angle - synonyms. (Steve's the best answer because he was first!) :) Actually no - there IS a VERY very very tiny difference, tiny difference - self confident is to be sure you are able to do things, self assured is the same confidence but you don't need other people to give it to you....... you back yourself up, you inspire and motivate yourself. So they're extremely closely related but there is a minute difference when you want there to be. But they're close enough to be synonymous with each other - I think

"Self-confident" isn't good usage. The word to use would be simply "confident." Comparing "confident" with "self-assured" (used as adjectives, not in a phrase like "confident that..."), the difference, if any, is very subtle. To me, "self-assured" has more of a connotation of confidence in a social context, whereas "confident" would be more general. He was a confident public speaker. He was a self-assured public speaker. He was a confident skier. Not: He was a self-assured skier. (You could say this, but it wouldn't sound natural.)

No difference -- these words are synonyms.

confidence is personal internal feeling of being assured but what is expressed in words is assurance. confidence can not be measured but assurance could be bound with in limit as words choosen by oneself to express....according to me more precisely "assurance is the measurement of confidence".