According to the Civil War Battles Page page on the battle 5,664 were killed in action (2,592 Confederate KIA, 3,072 Union KIA). Add to this Jenny Wade, a civilian in Gettysburg who was killed during the battle which brings the number to 5,665 killed. Now this is just KIA, it doesn’t include WIA (Wounded in Action) or MIA (Missing in Action) which combined comes up to 43,454 according to the page.
Now a National Park Service page on the battle entitled “The Battle of Gettysburg in Detail” puts the number much lower at just 16,000 killed, wounded, and captured. However a different NPS page on the battle puts this same number higher at 51,000. Note that this is a combined number of killed, wounded, and captured from both sides and not just those killed.
Then there’s the Military History Online’s casualty page on the battle. Like Civil War Battles Page it lists KIA, WIA, and MIA. For the Union the KIA number is listed at 3,155 while for the Confederacy this number is listed as being between 2,600 and 4,500. So this would mean a combined total of between 5,755 and 7,655. Plus Jenny Wade, of course. The combined army totals for KIA, WIA, and MIA is between 43,690 and 48,040 on this page.
74,845 people.