The word "gifted" has different meanings depending on the situation; for example different GT programs have different cutoffs. Some have cutoffs at the 99.9th percentile, some at the 90th.
Assuming a cutoff of a scaled test score of 130 for the "gifted" label, where that corresponds to two standard deviations from the mean, scores don't generally seem to be given in grade equivalents; instead grade equivalents are extrapolated loosely from scores, and the scores are the things that are most closely normalized to each other between different kinds of tests. That means that once you know what "gifted" means in a certain context (e.g. a scaled score of 130 or above on a particular test) the method that the test constructors use for grade equivalents, if there is one, would give your answer.
For this reason I think you would have to give the type of test and the gifted cutoff you're looking at for a full answer.
