Paul D. Simon wrote...
The following are a few of generally accepted values:

% of Population Number of Standard Deviations away from Mean
50.0% 0.674
68.3% 1.000
90.0% 1.645
95.0% 1.960
95.4% 2.000
99.7% 3.000
....

This is just one-tailed critical values from the standard normal
distribution. Use

=NORMSINV((1+pct)/2)

Note, however, that prior to Excel 2002 the NORMSINV function did a
poor job with values in the tail, so as a pratical matter, above 97.5%.