Casualties include three categories: 1) dead; 2) wounded; and 3) missing or captured.
Approximate Numbers
Union
Confederate
Total
Killed
2,100
1,550
3,650
Wounded
9,550
7,750
17,300
Missing/Captured
750
1,020
1,770
Total
12,400
10,320
22,720

These are the approximate numbers for September 17th, 1862. No one knows the actual number of men who would later die of their wounds or the number of missing who had been killed. If you take a conservative estimate of 20% of the wounded dying of their wounds and 30% of the missing killed, the approximate number of soldiers that died as a result of this battle are 7,640.
Casualties at Antietam by Phase of Battle
The casualty numbers below include all three categories. The numbers below are approximations of the casualties that occurred in each phase of the battle. The chaos of battle makes it exceedingly difficult to develop precise numbers for casualties in each phase of the battle. Overall, 1 in 4 soldiers involved in battle that day were killed, wounded, or missing.
Union Confederate
Troops Engaged
Casualties		 Troops Engaged
Casualties
Morning Phase
Cornfield 17,000 4,350 11,800 4,200
West Woods 5,400 2,200 9,000 1,850
Total, Morning Phase 22,400 6,550 20,800 6,050
Midday Phase
Bloody Lane 9,700 2,900 6,500 2,600
Afternoon Phase
Burnside Bridge 4,270 500 500 120
Final Attack 9,550 1,850 5,500 1,000
Total, Afternoon Phase 13,820 2,350 6,000 1,120
Battle Total* 56,000 12,400 37,400 10,300
*The total numbers for the battle do not reflect the sum of all three phases due to approximations for numbers in each phase.
Worst Civil War Battles
Antietam was the bloodiest one-day battle of the Civil War. But there were other battles,lasting more than one day, in which more men fell. The numbers below are total casualties for both sides.
(Source: The Civil War Dictionary, By Mark Boatner)

American Deaths in All Wars

The following numbers reflect deaths (excluding wounded and missing):
Source: U.S. Army Military History Institute, Carlisle, PA
Revolutionary War (1775-1783)
4,435
War of 1812 (1812-1815)
2,260
Mexican War (1846-1848)
13,283
Civil War (1861-1865)
623,026
Spanish-American War (1898)
2,446
World War I (1917-1918)
116,708
World War II (1941-1945)
407,316
Korean War (1950-1953)
36,914
Vietnam War (1964-1973)
58,169
Persian Gulf War (1991)
269
Last updated: 10/03/01, KBS