The total number of military and civilian casualties in World War I was about 40 million: estimates range from 18 to 22 million deaths and about 23 million wounded military personnel, ranking it among the deadliest conflicts.
The total number of deaths includes from 9 to 11 million military personnel. The civilian death toll was about 11 million, including nearly 8 million due to war-related famine and disease. The Triple Entente (also known as the Allies) lost about 6 million military personnel while the Central Powers lost about 4 million. At least 2 million died from diseases, and 6 million went missing, presumed dead. This article lists the casualties of the belligerent powers based on official published sources.
About two-thirds of military deaths in World War, I were in battle, unlike the conflicts in the 19th century when most deaths were due to disease. Nevertheless, diseases, including the 1918 flu pandemic and deaths while held as prisoners of war, still caused about one-third of total military deaths for all belligerents.