According to the National World War II Museum, 45 million civilians and 15 million combatants died during World War II. The number of soldiers wounded in battle was 25 million. These are estimates, and they are most likely low estimates.
It's possible that China suffered the greatest casualties during the war. Though the official number is 20 million for both combatants and civilians, the number may be as high as 50 million. China is followed by the Soviet Union, which suffered 24 million combined civilian and combatant deaths. After this is Germany, which suffered between 6.6 million and 8.8 million deaths; Japan, which lost between 2.6 million and 3.1 million people; and the Dutch East Indies, which suffered between 3 million and 4 million casualties.