The following table shows corresponding percentile scores for a range of Z scores.
PsyAsia's course attendees will recall that to calculate a Z score from a raw score one uses the following:
Z score = Raw Score minus Mean divided by Standard Deviation
To convert from any other standard score scale into a Z score one simply subtracts the mean of the other standard scale from the standard scale score and divides by the standard deviation of the standard score scale. So, to convert a T score into a Z score:
Z score = T Score minus mean of T score scale (50) divided by standard deviation of a T score scale (10).
See also: What is a percentile score