Location: Georgia
Confederate Commander: Braxton Bragg
Union Commander: William Rosecrans
Confederate Forces Engaged: 66,326
Union Forces Engaged: 58,222
Winner: Confederacy
Casualties: 34,624 (16,170 Union and 18,454 Confederate)
So, we've got about 35,000 casualties. Many of the battle reports are posted and I'll have to dig through them and figure out the KIA numbers, but they are surely large. This is at least a start in understanding the magnitude of what happened in Georgia in the fall of 1863.
Based on Trevor Dupuy's overall Civil War statistical averages, both Union and Confederate KIA numbers are low by about 20% (specifically the Union is 19% low and the Confederates 24% low). This doesn't necessarily imply the battle's reported casualties are wrong, just that they are skewed with respect to the "standard" KIA/WIA/DOW ratios. There were a large number of MIA's on both sides which could potentially explain the anomaly.