This is the commonly asked question now a days because NTA has specified the normalization procedure but has not shed any light on the specific data that have been used to arrive at the JEE Main percentile versus marks.

JEE Main Marks              Percentile

360 to 310                        100 - 99.98724751

309 to 299.                    99.985572 - 99.9740296

298 to 228.                    99.975891 - 99.7232942

227 to 198          99.73005678 - 99.65475792

197 to 188           99.4200875 - 99.28958392

187 to 178           99.26473052 - 99.07781811

177 to 168           99.06329703 - 98.85683701

167 to 158            98.82509541 - 98.55710695

157 to 148             98.53104347 - 98.20040957

147 to 138             98.14939961 - 97.75686494

137 to 128             97.69477799 - 97.17648701

127 to 118              97.13841571 - 96.41990133

117 to 108             96.35511496 - 95.49744019

107 to 98              95.42678954 - 94.40128456

97 to 88                94.19473145 - 92.74709113

87 to 78                 92.61891464 - 90.64227869

77 to 68                90.42902355 - 87.34180397

67 to 58                87.34180397 - 82.68016383

57 to 48                 81.92571907 - 75.39020758

47 to 38                74.13450619 - 64.11300382

37 to 28                62.88839244 - 49.28762915

27 to 18                 49.01228707 - 33.08815042

17 to 1.                   31.32570046 - 9.077538863

Hope this may help yoi