MedFriendly®

Standard Score to Percentile Conversion
The graph to the right is a
visual depicition of the
bell curve where the
mean is the middle of the
curve. Increments to the
right and left of the mean
are standard deviations
and provide information
on how far below or
above a score is from the
mean. The farther a score
is from the mean, the
more atypical it is.

Psychologists and teachers commonly use these scores when describing test
performance results. For example, you may have heard of someone having an IQ score
of 100. This called a standard score because you can see that 100 is at the exact
center of the curve. Z-scores, T scores, and scaled scores express the same thing that
standard scores do, but do so based on a different numerical system with different
means and standard deviation units as shown above. The percentage of people who
score is each standard deviation unit is noted in the bell curve above with % values.

RECOMMENDED STATISTICS BOOK: Statistics in Plain English
The percentile rank allows you to determine an
individual's position in relation to a sample of
other individuals. More specifically, the percentile
rank is the point in a distribution at or below which
the scores of a given percentage of individuals
fall. For example, a person with an IQ score of
120 (and a percentile rank of 91) has scored as
well or better than 91 percent of people in the
normal sample. The table below is intended for
general usage by health care providers and the
general public. For other measurements, please
visit the MedFriendly Measurements section.
 Z score Standard score Scaled score T score Percentile Interpretation 3.70 155 20 87 99.99 Very superior 3.65 155 20 86.5 99.99 Very superior 3.60 154 20 86 99.98 Very superior 3.55 153 20 85.5 99.98 Very superior 3.50 153 20 85 99.98 Very superior 3.45 152 20 84.5 99.97 Very superior 3.40 151 20 84 99.97 Very superior 3.35 150 20 83.5 99.96 Very superior 3.30 150 20 83 99.96 Very superior 3.25 149 20 82.5 99.95 Very superior 3.20 148 20 82 99.93 Very superior 3.15 147 19 81.5 99.91 Very superior Z score Standard score Scaled score T score Percentile Interpretation 3.10 147 19 81 99.91 Very superior 3.05 146 19 80.5 99.89 Very superior 3.00 145 19 80 99.87 Very superior 2.95 144 19 79.5 99.83 Very superior 2.90 144 19 79 99.83 Very superior 2.85 143 18 78.5 99.79 Very superior 2.80 142 18 78 99.74 Very superior 2.75 141 18 77.5 99.69 Very superior 2.70 141 18 77 99.69 Very superior 2.65 140 18 76.5 99.62 Very superior 2.60 139 18 76 99.53 Very superior 2.55 138 17 75.5 99 Very superior Z score Standard score Scaled score T score Percentile Interpretation 2.50 138 17 75 99 Very superior 2.45 137 17 74.5 99 Very superior 2.40 136 17 74 99 Very superior 2.35 135 17 73.5 99 Very superior 2.30 135 17 73 99 Very superior 2.25 134 17 72.5 99 Very superior 2.20 133 17 72 99 Very superior 2.15 132 16 71.5 98 Very superior 2.10 132 16 71 98 Very superior 2.05 131 16 70.5 98 Very superior 2.00 130 16 70 98 Very superior 1.95 129 16 69.5 97 Superior 1.90 129 16 69 97 Superior Z score Standard score Scaled score T score Percentile Interpretation 1.85 128 16 68.5 97 Superior 1.80 127 15 68 96 Superior 1.75 126 15 67.5 96 Superior 1.70 126 15 67 96 Superior 1.65 125 15 66.5 95 Superior 1.60 124 15 66 95 Superior 1.55 123 14 65.5 94 Superior 1.50 123 14 65 94 Superior 1.45 122 14 64.5 93 Superior 1.40 121 14 64 92 Superior 1.35 120 14 63.5 91 Superior 1.30 120 14 63 91 Superior 1.25 119 14 62.5 90 High average Z score Standard score Scaled score T score Percentile Interpretation 1.20 118 14 62 88 High average 1.15 117 13 61.5 87 High average 1.10 117 13 61 87 High average 1.05 116 13 60.5 86 High average 1.00 115 13 60 84 High average 0.95 114 13 59.5 82 High average 0.90 114 12 59 82 High average 0.85 113 12 58.5 81 High average 0.80 112 12 58 79 High average 0.75 111 12 57.5 77 High average 0.70 111 12 57 77 High average 0.65 110 12 56.5 75 High average 0.60 109 12 56 73 Average Z score Standard score Scaled score T score Percentile Interpretation 0.55 108 12 55.5 70 Average 0.50 108 11 55 70 Average 0.45 107 11 54.5 68 Average 0.40 106 11 54 66 Average 0.35 105 11 53.5 63 Average 0.30 104 11 53 61 Average 0.25 104 11 52.5 61 Average 0.20 103 11 52 58 Average 0.15 102 10 51.5 55 Average 0.10 102 10 51 55 Average 0.05 101 10 50.5 53 Average 0 100 10 50 50 Average Z score Standard score Scaled score T score Percentile Interpretation -0.05 99 10 49.5 47 Average -0.10 98 9 49 45 Average -0.15 98 9 48.5 45 Average -0.20 97 9 48 42 Average -0.25 96 9 47.5 39 Average -0.30 96 9 47 39 Average -0.35 95 9 46.5 37 Average -0.40 94 9 46 34 Average -0.45 93 8 45.5 32 Average -0.50 93 8 45 32 Average -0.55 92 8 44.5 30 Average -0.60 91 8 44 27 Average Z score Standard score Scaled score T score Percentile Interpretation -0.65 90 8 43.5 25 Average -0.70 90 8 43 25 Average -0.75 89 8 42.5 23 Low average -0.80 88 8 42 21 Low average -0.85 87 7 41.5 19 Low average -0.90 87 7 41 19 Low average -0.95 86 7 40.5 18 Low average -1.00 85 7 40 16 Low average -1.05 84 7 39.5 14 Low average -1.10 84 7 39 14 Low average -1.15 83 6 38.5 13 Low average -1.20 82 6 38 12 Low average Z score Standard score Scaled score T score Percentile Interpretation -1.25 81 6 37.5 10 Low average -1.30 81 6 37 10 Low average -1.35 80 6 36.5 9 Low average -1.40 79 6 36 8 Borderline -1.45 78 6 35.5 7 Borderline -1.50 78 6 35 7 Borderline -1.55 77 5 34.5 6 Borderline -1.60 76 5 34 5 Borderline -1.65 75 5 33.5 5 Borderline -1.70 75 5 33 5 Borderline -1.75 74 5 32.5 4 Borderline -1.80 73 5 32 4 Borderline -1.85 72 5 31.5 3 Borderline Z score Standard score Scaled score T score Percentile Interpretation -1.90 72 5 31 3 Borderline -1.95 71 4 30.5 3 Borderline -2.00 70 4 30 2 Borderline -2.05 69 4 29.5 2 Inferior -2.10 69 4 29 2 Interior -2.15 68 4 28.5 2 Inferior -2.20 67 3 28 1 Inferior -2.25 66 3 27.5 1 Inferior -2.30 66 3 27 1 Inferior -2.35 65 3 26.5 1 Inferior -2.40 64 3 26 1 Inferior -2.45 63 3 25.5 1 Inferior Z score Standard score Scaled score T score Percentile Interpretation -2.50 63 3 25 1 Inferior -2.55 62 3 24.5 1 Inferior -2.60 61 2 24 0.47 Inferior -2.65 60 2 23.5 0.38 Inferior -2.70 60 2 23 0.38 Inferior -2.75 59 2 22.5 0.31 Inferior -2.80 58 2 22 0.26 Inferior -2.85 57 1 21.5 0.21 Inferior -2.90 57 1 21 0.21 Inferior -2.95 56 1 20.5 0.17 Inferior -3.00 55 1 20 0.13 Inferior -3.05 54 1 19.5 0.11 Inferior Z score Standard score Scaled score T score Percentile Interpretation -3.10 54 1 19 0.11 Inferior -3.15 53 0 18.5 0.09 Inferior -3.20 52 0 18 0.07 Inferior -3.25 51 0 17.5 0.05 Inferior -3.30 51 0 17 0.05 Inferior -3.35 50 0 16.5 0.04 Inferior -3.40 49 0 16 0.03 Inferior -3.45 48 0 15.5 0.03 Inferior -3.50 48 0 15 0.03 Inferior -3.55 47 0 14.5 0.02 Inferior -3.60 46 0 14 0.02 Inferior -3.65 45 0 13.5 0.01 Inferior