He will be charged with 24 counts of murder and 116 counts of attempted murder. You can see the full court complaint against him here.
Holmes is suspected of opening fire on a crowd at a midnight screening of The Dark Knight Rises in Aurora, Colorado, killing 12 and injuring 58. There are two counts of murder for every person dead — 12 for first-degree murder, and 12 for murder with extreme indifference. Holmes will also be charged with one count of possession of explosives for his booby-trapped apartment.